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The  PRACTICAL 

OPERATION 

of  ARC  LAMPS 


NATIONAL  CARBON  COMPANY 

CLEVELAND,    OHIO 

1911 


1 


Copyright,    1911 

by 
National    Carbon    Company 


PREFACE 

/TTHERE  is  no  more  reliable  piece  of  electrical  apparatus 
^  than  the  arc  lamp.  With  proper  care,  suitable  car- 
bons, and  a  uniform  supply  of  power,  it  can  be  depended 
upon  to  meet  its  requirements,  but  any  apparatus  exposed 
to  such  hard  usage  as  the  arc  lamp  will  sooner  or  later 
develop  deficiencies  which,  if  not  promptly  rectified,  may 
lead  to  serious  complications.  It  is  with  the  idea  of  giving 
a  few  suggestions,  of  laying  down  a  few  rules,  which, 
if  followed,  will  increase  the  efficiency  and  raise  the 
standard  of  arc  lighting  systems,  that  this  book  has  been 
prepared.  The  suggestions  offered  are  necessarily  of  a 
very  general  nature,  since  they  refer  to  lamps  of  no 
particular  manufacture  and  are  equally  applicable  to  all 
types.  The  authors  have  been  associated  with  the 
Engineering  Department  of  the  National  Carbon  Company 
for  a  great  many  years,  and  their  close  contact  with  all 
types  of  arc  lamps,  all  brands  of  carbons,  and  all  arc 
systems,  should,  perhaps,  enable  them  to  take  a  more 
comprehensive  view  of  common  arc  lamp  practice  than 
Engineers  who  are  more  directly  interested  in  the  develop- 
ment of  some  particular  type.  They  will  be  pleased  to 
take  up  individually  any  problem  of  daily  practice  which 
may  not  be  covered  by  the  suggestions  outlined  in  this 
book. 


NATIONAL  CARBON  COMPANY 

PUBLICITY   DIVISION 
1911 


215437 


Enclosed  Arc  Lamps 

Enclosed  arc  lamps  may  be  divided  injbo  three,  general 
types,  the  multiple  or  constant  potential^  i'he  gesies  or 
constant  current,  and  the  series  multiple  or  power  cjxcuit 
lamps.  Each  of  these  types  is  designed  to  meet  cei'tain 
service  conditions.  All  three  types  are  made  fxjx  ^ithe/ 
direct  or  alternating  current.  D.  C.  lamps  are  preiWable, 
due  to  their  higher  light  efficiency  and  longer  lifa^  but 
the  A.  C.  lamps  are  very  often  more  desirable  becpuse 
of  the  more  efficient  transformation  and  transmission  ol 
electrical  energy  possible  in  A.  C.  systems. 

MULTIPLE  ARC  LAMPS.  Multiple  lamps  are  in 
very  extensive  use  at  present  and  are  especially  popular 
for  indoor  lighting  on  account  of  the  low  voltage 
required.  They  may  be  connected  directly  across  110 
and  sometimes  on  220  volt  circuits. 

Figure  1  shows  the  connections  for  a  D.  C.  multiple 
lamp.  There  is  only  one  set  of  magnet 
coils,  R  and  S,  and  these  are  con- 
nected in  series  with  each  other  and  in 
series  with  the  arc.  These  coils  pull 
directly  on  the  armature  P,  which 
operates  the  clutch  C  controlling  the 
upper  carbon.  The  operation  of  the 
lamp  is  as  follows:  When  the  current 
is  first  switched  on,  the  carbons  are 
touching  each  other  and  a  strong  cur- 
rent flows  through  the  magnet  coils. 
This  attracts  the  armature  P,  raising 
the  upper  carbon  and  forming  the  arc. 
The  current  decreases  as  the  carbons 
are  separated  until,  when  the  arc  is  the 
proper  length,  the  .magnets  are  not 
strong  enough  to  raise  the  upper  car- 
bon further.  As  the  carbons  are 
burned  away  the  magnets  are  weakened  and  the  clutch 

5 


rod  slowly  descends  until  the  clutch  strikes  the  stop  and 
allows  the\  caVb^Xo.  to  slip  downward.  The  resistance  B, 
at  the  top  of  t  t<he  lamp,  is  used  to  cut  down  the  line  vol- 
tage to i  th&t  'required  for  the  arc.  The  110  to  125  volt 
D.  0.  lamp  operates  best  with  an  arc  voltage  of  about  80. 
Thic  resistance  is  made  of  German-silver  wire  wound 
on  a  porcelain  spool.  To  regulate  it,  the  clip  F  is  slipped 
up  and  down  along  the  guide  rod.  In  addition  to  cutting 
dovrii  the  line  voltage  to  that  required  for  the  arc  this 
resistance  serves  to  steady  the  light  so  that  small  changes 
vdii'  the  length  of  the  arc  will  not  cause  such  great  varia- 
tions. It  also  prevents  the  lamp  from  being  short  cir- 
cuited when  the  carbons  are  in  contact.  Although  not 
shown  in  the  figure,  a  dash  pot  should  be  provided  to 
deaden  the  movement  of  the  regulating  mechanism,  which 
results  in  a  steadier  arc  and  more  constant  illumination. 
The  magnet  coils  are  sometimes  provided  with  taps  on 
each  coil  to  adjust  the  lamp  to  burn  at  different  current 
strengths.  The  lamp  shown  in  the  figure  has  three  taps, 
1-2-3,  in  each  coil.  In  another  form  of  lamp  the  current 
strength  is  adjusted  by  means  of  small  weights  placed 
on  top  of  the  upper  carbon  holder.  The  switch  on  the 
top  of  the  lamp  is  used  to  open  the  circuit  when  any 
repairs  or  adjustments  are  being  made.  The  upper  car- 
bon holder  slides  within  a  tube  and  connection  is  usually 
made  to  it  by  a  flexible  cable.  In  the  lamp  shown  in 
Fig.  1  this  tube  has  a  slot  in  its  side  and  through  it  an 
extension  of  the  carbon  holder  projects.  To  this  the 
flexible  cable  is  connected.  In  another  form  the  flexible 
cable  is  run  directly  from  one  of  the  binding  posts  of 
the  lamp  into  the  top  of  the  tube  and  no  slot  is  required. 
A  third  lamp  has  no  tube  but  is  supplied  with  two  guide 
rods  on  which  the  carbon  holder  slides.  The  carbon 
holder  consists  of  a  three-jaw  spring  clutch  which  grips 
the  end  of  the  carbon. 

Many  forms   of  clutches   are   used.     They   are  usually 
made   wholly   of  metal,   though   a   metal   ring   lined   with 


a  porcelain  bushing  is  sometimes  used.  One  of  the  most 
common  forms  of  clutch  consists  of  two  clamping  rings 
around  the  carbon,  the  lower  ring  being  supported  by 
the  upper.  Another  form  consists  of  a  metal  sleeve  with 
a  clamping  lever  at  one  side. 

For  220-250  volt  D.  C.  cir- 
cuits two  types  of  lamps  are 
available.  One,  with  a  single 
pair  of  carbons  burns  with  an 
arc  voltage  of  140-150.  The 
second,  called  a  Twin  Carbon 
lamp,  uses  two  pairs  of  elec- 
trodes placed  side  by  side  and 
connected  in  series  as  shown 
in  Fig.  2.  Both  pairs  of  car- 
bons are  controlled  by  the 
same  regulating  mechanism. 
The  best  results  will  be 
obtained  if  the  lamp  is 
adjusted  for  80  volts  at  each 
arc. 

A.  C.  lamps  may  be  operated  on  circuits  of  any  fre- 
quency from  25  to  140  cycles.  The  standard  for  lighting 
is  60  cycles,  and  lamps  operating  on  this  frequency  give 
better  service  than  on  the  lower  values  wjiere  flickering 
is  liable  to  occur.  With  frequency  much  above  70  cycles 
the  operation  of  the  lamp  is  liable  to  become  noisy. 

The  A.  C.  multiple  lamp,  shown  in  Fig.  3,  operates 
on  exactly  the  same  principle  as  the  D.  C.  There  are 
some  points  about  its  construction,  however,  that  are 
radically  different.  For  a  regulating  resistance,  a  choke 
coil  instead  of  a  German-silver  wire  resistance  is  used. 
This  cuts  down  the  line  voltage  just  as  a  resistance 
would,  but  does  not  consume  nearly  as  much  power.  It 
consists  of  a  number  of  coils  of  copper  wire  wound  on 
an  iron  core  and  connected  in  series  with  each  other. 
By  varying  the  number  of  coils  connected  in  series  with 


the  arc,  the  arc  voltage  may  be  varied. 

Referring  to  Fig.  3,  all  the  coils  except 

AB  give  an  adjustment  of  3  to  4  volts. 

This  is  a  half  coil  and  gives  a  change 

of  2  volts,  so  by  always  keeping  one  lead 

on  tap  A  or  B  close  adjustment  can  be 

obtained.     By  means  of  this  choke  coil 

lamps   may  be   adjusted  to   operate   on 

different  frequencies  as  well  as  for  dif- 
ferent   values    of    line    voltage    on    the 

same  frequency.     Other  adjustment  in 

the  lamp  mechanism  will  usually  have 

to  be  made  for  changes  in  the  frequency 

or  current. 

This  type  of  lamp  is  used  on  110-120 

volt  circuits  only  and  burns  with  an  arc 

voltage  of  72.     All  the  magnet  cores  of 

the  lamp  are   made  of  laminated  iron, 

i.  e.,  of  thin  sheets  of  iron  riveted 
together.  The  constant  reversal  of 
the  direction  of  the  magnetism 
when  AC  is  used  would  induce 
currents  in  solid  cores  which  would 
weaken  the  magnetic  effect  and 
also  cause  heating.  In  the  D.  C. 
lamp  these  parts  are  made  solid. 

For  220  and  440  volt  A.  C.  cir- 
cuits, self-contained  lamps  using  an 
auto  transformer  instead  of  a  choke 
coil  can  be  obtained.  The  auto 
transformer  consists  of  a  number 
of  small  separate  coils  mounted  on 
a  ring  shaped  core  of  laminated 
iron.  The  voltage  adjustment  is 
made  by  means  of  taps  from  one  of 
the  transformer  coils  to  which  a 

flexible  lead  is  connected.     Tf  sufficient  change  in  voltage 

8 


cannot  be  obtained  in  this  way,  the  terminals  of  the  lamp 
may  be  shifted  to  another  coil.  The  connections  of  this 
lamp  are  shown  in  Pig*  4. 
SERIES  ARC  LAMPS. 
Series  arc  lamps  are  used 
chiefly  for  street  or  other 
outdoor  lighting  and  for 
industrial  plants.  As  many 
as  100  enclosed  arc  lamps 
are  connected  in  series  on 
one  circuit.  This  would  give 
a  voltage  of  100x75=7500 
across  the  terminals  of  the 
circuit  assuming  a  lamp 
voltage  of  75.  The  line 
current  is  held  at  a  con- 
stant value  by  apparatus  in 
the  power  house  or  sub- 
station  (see  page  35). 
Since  the  current  is  the 
same,  no  matter  what  the 
length  of  the  arc,  it  is  evident  that  a 
series  coil  alone  cannot  regulate  this  lamp. 
Fig.  5  shows  the  connections,  for  an  A.  0. 
series  lamp.  Owing  to  the  difficulty  of  generating  D.  C.  at 
the  high  voltage  required,  comparatively  few  D.  C.  series 
lamps  are  being  installed.  The  two  magnets,  A  and  B, 
operate  the  pivoted  lever  F,  to  which  the  clutch  rod  is 
connected.  The  coil  A  is  connected  in  series  with  the 
arc,  while  B  is  connected  in  shunt  across  the  arc.  The 
series  coil  tends  to  separate  the  carbons  and  the  shunt 
coil  to  allow  them  to  come  together.  The  resistance  H, 
called  the  starting  resistance,  is  connected  across  the 
terminals  of  the  lamp  through  the  cut-out  K,  which  is 
operated  from  the  lever  F.  When  the  current  is  turned 
on  the  carbons  are  in  contact  and  part  of  the  current 
flows  through  the  series  coil  and  the  rest  through  the 
starting  resistance.  The  series  magnet  pulls  up  its  end  of 


the  lever  separating  the  carbons  and  opening  the  cut- 
out K.  As  the  carbons  are  separated  the  voltage 
across  the  arc  rises  and  strengthens  the  shunt  coil  until 
when  the  proper  length  of  the  arc  is  reached  it  equalizes 
the  series  magnet.  As  the  carbons  are  consumed  the  shunt 
magnet  becomes  stronger  than  the  series  and  lowers  the 
carbon.  If  the  carbon  fails  to  feed  and  the  arc  becomes 
too  long,  the  shunt  magnet  will  pull  up  its  end  of  the  lever 
until  it  closes  the  cut-out  K.  The  switch  S  is  used  for 
short-circuiting  the  lamp  while 
making  repairs.  To  adjust  this 
lamp  to  operate  with  different 
values  of  line  current,  the 
**,„  weight  M  on  the  pivoted 
lever  is  slipped  along  its  guides. 
In  some  lamps  this  adjustment  is 
made  by  a  resistance  shunted 
across  the  series  coil,  as  shown  in 
Fig.  6.  In  this  lamp  both  coils 
have  a  shunt  and  a  series  winding. 
The  dash  pot  D  is  used  to  steady 
the  movement  of  the  clutch  lever. 
The  carbon  holder  and  clutch  are 
like  those  used  in  the  multiple 
lamp.  The  series  lamps  need  no 
adjusting  resistance  in  series  with  the  arc. 

SERIES  MULTIPLE  ARC  LAMPS.  Series  multiple,  or 
power  circuit  lamps,  are  usually  operated  two  in  series  on 
220  volt  circuits,  or  five  in  series  on  500  volt  circuits. 
They  are  used  extensively  on  D.  C.  motor  circuits, 
especially  for  lighting  shops  or  parks  on  electric  railway 
lines  where  only  the  500  volt  power  from  the  trolley  is 
available.  One  form  of  this  type  is  very  similar  to  the 
series,  except  that  they  are  supplied  with  a  compensating 
resistance  equivalent  to  that  of  the  arc.  When  a  lamp 
goes  out  for  any  reason  this  compensating  resistance  is 
switched  in  so  that  the  other  lamps  in  series  with  it  will 


not  be  affected.  This  resistance  is  connected  in  series 
with  a  cut-out  controlled  by  the  shunt  coil  in  exactly  the 
same  way  as  the  starting  resistance  in  the  series  lamp. 
The  lamp  is  also  supplied  with  a  regulating  resistance  in 
series  with  the  arc.  Each  lamp  of  the  set  is  adjusted 
to  consume  its  proper  proportion  of  the  voltage.  For 
example,  with  two  lamps  in  series  on  a  220  volt  circuit 
with  an  arc  voltage  of  80,  each  lamp  should  consume 
110  volts,  so  the  regulating  resistance  should  be  adjusted 
for  30  volts. 

Another  form  of  series  multiple  lamp  is  the  same  as  the 
multiple,  except  that  it  has  a  small  equalizing  weight 
attached  to  the  clutch  mechanism,  in  such  a  way  as  to 
neutralize  any  tendency  which  one  lamp  in  the  series 
may  have  to  take  more  than  its  share  of  voltage. 

MINIATURE  AND  INTENSIFIED  ARC  LAMPS.  In 
the  last  few  years  many  types  of  arc  lamps  burning  small 
carbons  (about  ^4-inch  in  diameter)  have  been  put  on 
the  market.  These  lamps  are  the  result  of  the  demand 
for  a  high  efficiency  lighting  unit,  and  are  intended 
primarily  for  interior  lighting.  They  are  all  multiple 
lamps  and  most  of  them  are  made  for  D.  C.  circuits  only, 
but  there  are  several  A.  C.  lamps  of  this  type.  The 
regulating  mechanism  of  most  of  these  lamps  resembles 
that  of  the  multiple  lamps  already  described.  One  lamp 
of  this  type,  however,  is  radically  different.  Three  car- 
bons are  used.  The  two  upper  carbons  are  of  small  size 
inclined  towards  each  other  and  touching  at  their  lower 
ends.  The  arc  is  thus  maintained  without  the  aid  of  any 
regulating  mechanism.  The  lower  carbon  is  of  larger 
size  and  is  fed  upward  by  means  of  a  series  coil,  main- 
taining the  arc  in  a  fixed  position.  The  two  upper  car- 
bons are  burned  alternately.  The  lamps  of  this  type  are 
called  Miniature,  Small  Arcs  and  Semi-Enclosed  by  differ- 
ent manufacturers.  They  owe  their  high  efficiency 
primarily  to  the  small  diameter  of  the  carbons  used. 
This  causes  a  relatively  high  current  density  and  a  high 

11 


degree  of  incandescence  at  the  tip  of  the  carbon.  Heat 
is  not  as  readily  carried  away  by  the  small  carbons  as 
by  the  larger  ones  of  the  enclosed  arc.  The  arc  is  steadier 
and  does  not  wander  over  the  end  of  the  carbons  as  in 
enclosed  lamps.  Cored  carbons  are  used.  The  light 
obtained  from  these  lamps  is  pure  white  and  is  one  of 
the  best  known  substitutes  for  daylight.  The  bluish  tinge 
noticeable  in  the  enclosed  lamp  is  entirely  absent.  This 
makes  the  lamps  particularly  well  suited  for  lighting 
stores  and  other  places  where  color  matching  is  important. 
The  manufacturers  have  spent  much  time  in  designing 
the  case  and  globe  equipment  and  supply  their  lamps  in 
most  attractive  forms  which  would  add  to  the  decora- 
tion in  any  building.  A  special  feature  of  one  of  these 
lamps  is  that  it  is  provided  with  a  terminal  so  that  it 
may  be  screwed  into  an  incandescent  lamp  socket. 

These  lamps  may  be  procured  for  110  volt  D.  C.  and 
A.  C.  and  for  220  volt  D.  C.  circuits. 

GLOBE  AND  REFLECTOR  EQUIPMENT.  This  will 
naturally  be  governed  by  general  conditions.  The  stand- 
ard equipment  consists  of  a  light  opal  inner  and  clear 
outer  globe.  The  advantage  of  the  light  opal  inner  globe 
is  that  the  opal  globe  becomes  luminous  and  forms  a 
secondary  source  of  diffused  light  which  eliminates 
shadows,  and  at  the  same  time  gives  a  more  effective 
light  due  to  the  better  distribution.  For  interior  work, 
there  is  the  further  advantage  that  the  violet  rays  are 
partly  absorbed,  thus  making  a  whiter  light. 

Two  clear  globes  should  not  be  used  except  for  photo- 
graphic work  where  a  light  is  required  which  is  high  in 
actinic  value.  Special  conditions  sometimes  call  for  other 
combinations,  such  as  clear  inner  and  opal  outer,  etc.  In 
a  number  of  cases  no  outer  globe  is  needed. 

For  A.  C.  lamps  a  reflector  is  usually  used,  either  with 
or  without  an  outer  globe.  A  considerable  portion  of  the 
light  from  an  A.  C.  arc  is  thrown  upward,  and  if  no 
reflector  were  used,  this  light  would  be  lost. 

12 


General  Rules  for  Operation  and  Care 
of  Enclosed  Arc  Lamps 

Only  those  rules  which  apply  to  all  types  of  arc  lamps 
can  be  given.  Further  information  on  any  particular  type 
can  be  obtained  from  the  instruction  books  of  the  manu- 
facturers. 

CARBONS.  In  order  to  obtain  satisfactory  operation 
of  enclosed  arc  lamps,  only  high  grade  carbons  should  be 
used.  They  should  be  straight,  round  and  of  uniform 
diameter,  being  free  from  blisters  and  dirty  spots.  Should 
these  spots  be  present,  they  should  be  removed  with 
sand  paper  before  the  carbons  are  inserted  in  the  lamp. 
COLUMBIA  carbons,  manufactured  by  the  National  Car- 
bon Company,  Cleveland,  Ohio,  have  given  excellent  satis- 
faction in  practically  all  cases  where  they  have  been  tried. 
Their  manufacture  is  closely  watched  and  controlled  by 
an  elaborate  testing  system  which  eliminates  the  possi- 
bility of  crooked,  blistered,  or  dirty  carbons  reaching  the 
trimmers7  hands.  The  raw  materials  used  are  of  the 
highest  obtainable  purity  and  are  constantly  kept  at  this 
standard  by  frequent  chemical  analyses. 

Carbons  should  be  stored  in  a  dry  place.  Do  not  place 
boxes  of  carbons  for  any  length  of  time  on  a  cement 
floor  having  an  earth  foundation.  If  they  must  be  stored 
in  such  a  place,  put  boards  under  them  so  as  to  allow 
free  circulation  of  air. 

Trimmers  should  use  a  covered  bag  to  protect  the  car- 
bons from  dust  and  dampness.  Burned  carbons,  cleaning 
cloths,  or  other  material  should  not  be  allowed  to  come 
in  contact  with  the  carbons. 

For  D.  C.  lamps  solid  carbons  should  be  used  almost 
invariably,  with  the  exception  of  the  miniature  and  other 
small  lamps,  which  use  as  a  rule  two  cored  carbons.  Most 
enclosed  arc  lamps  are  designed  to  burn  upper  carbons 
12  inches  long  and  in  practically  all  cases  the  stub  left 
over  from  the  upper  carbon  is  used  for  the  lower  of  the 

13 


next  trim.  This  should  be  from  4^  to  6  inches  long, 
as  specified  by  the  manufacturer.  About  3  to  4  inches  of 
lower  carbon  is  consumed  per  trim,  so  it  is  evident  that 
the  number  of  hours  burning  per  inch  of  lower  carbon  is 
high.  To  a  trimmer  cutting  off  carbons,  ^-inch  will  not 
appear  of  much  importance,  but  in  a  lamp  burning  150 
hours  it  will  mean  a  life  of  about  10  to  12  hours.  Some 
arrangements  should  be  made  for  cutting  off  carbons  the 
proper  length.  This  can  readily  be  done  at  the  station. 
If  the  lower  carbon  is  too  long  it  is  liable  to  cause  break- 
age of  the  inner  globe  or  melting  of  the  gas  cap.  A  large 
percentage  of  inner  globe  breakage  occurs  during  the 
first  15  minutes  of  burning  after  retrimming.  This  is 
when  the  lower  carbon  is  at  its  maximum  length,  with 
the  arc  near  the  top  of  the  globe,  and  at  the  same  time 
the  globe  is  undergoing  a  large  temperature  change.  On 
the  other  hand,  if  the  lower  carbon  is  too  short,  it  will 
burn  down  into  the  carbon  holder. 

In  cutting  the  old  upper  carbon  for  the  lower  of  the 
next  trim,  the  end  which  has  been  in  the  upper  holder 
should  be  cut  off  and  the  carbon  placed  in  the  lamp  with 
the  burned  end  to  the  arc.  This  brings  the  lamp  to  full 
candle  power  in  a  minimum  length  of  time  and  sometimes 
prevents  flaming  and  possible  globe  breakage. 

In  the  D.  C.  lamp  the  upper  carbon  should  always  be 
positive,  since  it  is  consumed  more  rapidly.  If  the  lower 
carbon  were  positive,  it  would  be  consumed  in  a  short 
time,  the  carbon  holder  would  be  destroyed  and  the  globe 
melted.  With  the  positive  carbon  at  the  bottom,  most 
of  the  light  is  thrown  upward  and  not  downward.  To 
test  for  the  polarity  of  a  lamp,  allow  it  to  burn  for  a  few 
minutes,  then  turn  it  off.  The  hotter  carbon,  i.  e.,  the 
one  remaining  red  longer,  is  the  positive. 

For  A.  C.  lamps  one  cored  and  one  solid  carbon  are  used, 
but  on  circuits  where  the  voltage  and  frequency  vary 
considerably,  two  cored  carbons  will  often  give  better 
results.  The  lower  carbon  should  be  from  5%  to  7  inches 


long.  In  this  type  of  lamp  both  carbons  are  consumed  at 
about  the  same  rate. 

The  A.  C.  lamp,  as  a  rule,  uses  a  Q1/^  or  12  inch  upper 
carbon. 

In  trimming  an  arc  lamp  the  upper  carbon  should  be 
pushed  up  as  far  as  it  will  go  in  order  to  make  good 
contact  with  the  holder.  Carbons  with  slightly  beveled 
ends  will  facilitate  this  operation.  The  carbon  should 
slide  through  the  clutch  and  the  bushing  of  the  gas  cap 
freely.  After  trimming,  the  clutch  should  be  able  to 
separate  the  carbons,  about  1  inch  in  the  case  of  the 
multiple  lamps  and  ^  inch  in  the  series.  If  the  carbons 
cannot  be  separated  far  enough,  it  will  cause  high  cur- 
rent in  the  multiple  lamps,  which  may  blow  the  fuse  or 
possibly  burn  out  a  coil,  while  the  series  lamps  will 
operate  with  a  short  arc  which  will  cause  globe  blacken- 
ing. To  test  a  lamp  after  trimming  lift  the  clutch  by 
pushing  on  the  rod  leading  to  the  magnets.  Lifting  the 
carbons  is  only  half  a  test. 

GLOBES.  The  inner  globe  should  be  thoroughly  cleaned 
at  every  trimming.  Most  of  the  large  operators  of  arc 
lamps  are  doing  this  work  at  a  central  globe  cleaning 
plant.  Duplicate  sets  of  inner  globes  and,  with  lamps 
with  detachable  holders,  of  lower  holders  are  provided. 
All  globes  are  washed  at  the  station.  Soap  is  not  required 
and,  if  it  is  used,  the  globes  should  be  thoroughly  rinsed 
in  clean  water.  The  grease  from  the  soap  if  left  in  the 
globe  may  cause  blackening.  If  the  number  of  globes  to 
be  washed  each  day  is  large,  the  work  can  be  facilitated 
by  the  use  of  a  revolving  brush,  running  under  water,  or 
with  a  continuous  stream  of  water  supplied  to  it.  The 
lower  carbons  are  cut  to  size  at  the  station  and  when- 
ever possible  the  lower  carbon  and  inner  globe  are 
assembled  in  the  holder.  The  globes  are  then  packed  in 
partitioned  baskets  or  boxes,  which  the  trimmer  carries 
around  in  a  wagon.  In  trimming  he  has  simply  to  sup- 
ply a  new  upper  carbon  and  replace  the  dirty  globe  with 

15 


a  clean  one.  If  the  lower  carbon  holders  are  not  detach 
able,  the  lower  carbon  and  the  clean  globe  must  be  fitted 
into  the  holder  at  the  lamp.  Central  station  globe  clean- 
ing is  advisable  whenever  the  size  of  the  installation 
allows  it. 

When  globes  are  cleaned  on  the  street,  two  cloths 
should  be  used,  one  wet  for  washing  the  globes  and  the 
other  for  drying.  The  wet  cloth  should  be  rinsed  fre- 
quently in  clean  water. 

If  the  deposit  sticks  to  the  globe  it  can  be  readily 
removed  by  a  weak  solution  of  muriatic  acid. 

GAS  CAPS.  Gas  caps  should  be  kept  clean.  Other- 
wise the  deposit  from  the  gas  caps  will  form  on  the 
inner  globe.  Corrosion  or  dirt  on  the  gas  cap  always 
produces  short  life,  since  it  is  impossible  to  seat  the 
inner  globe  properly. 

Gas  checks  or  vents  should  be  kept  clean  at  all  times. 
If  possible,  blow  out  this  dust.  A  small  pair  of  bellows 
may  be  used  to  advantage  in  cleaning  gas  checks.  If  an 
attempt  is  made  to  clean  the  vents  with  a  stick,  the 
deposit  is  more  likely  to  be  packed  into  the  vent  than 
to  be  removed  from  it. 

In  lamps  with  removable  gas  caps,  it  is  well  to  replace 
the  caps  at  regular  intervals  of  a  month  or  more  and 
return  the  used  caps  to  the  station  for  a  thorough  clean- 
ing. With  this  type  of  gas  cap,  trouble  has  resulted  due 
to  the  supporting  hook  being  bent  or  becoming  loose. 
This  forces  the  cap  out  of  place,  causing  the  carbons  to 
bind.  This  same  trouble  is  caused  by  the  lower  lamp 
frame  springing. 

Considerable  trouble  is  encountered  due  to  warped  or 
cracked  gas  caps. 

CAEBON  LIFE.  In  order  to  obtain  long  •  life,  it  is 
necessary  that  the  inner  globe  should  be  air  tight.  Open 
base  globes  as  a  rule  will  give  longer  life  than  closed 
base  by  about  20  to  25  hours.  This  is  due  to  the  fact 
that  the  open  base  globe  is  smaller,  and  therefore  con- 
ic 


tains  less  air,  initially.  The  tendency  for  leakage  in  the 
two  types  is  about  the  same,  for  while  the  open  base  globe 
has  two  openings,  the  closed  base  has  a  larger  leakage 
surface  at  the  top. 

When  using  open  base  globes  care  should  be  taken  to 
set  the  globe  properly  to  exclude  the  air.  The  globe  rests 
on  an  asbestos  washer  in  the  lower  carbon  holder.  An 
old,  hard  washer  keeps  out  the  air  better  than  a  new  one, 
so  it  should  be  renewed  only  when  worn  out  or  torn.  If 
•the  edge  of  the  globe  is  kept  free  from  chips,  a  washer 
should  last  for  years.  When  replacing  washers,  the  old 
one  should  be  removed  and  the  holder  cleaned  before  a 
new  washer  is  inserted. 

In  setting  globes  supported  by  a  bail,  turn  the  globe 
until  it  will  not  rock.  If  such  a  position  cannot  be 
found,  the  seat  of  the  gas  cap  must  be  cleaned  and  trued 
up  before  normal  carbon  life  can  be  obtained. 

A  nicked  or  cracked  globe  will  reduce  the  carbon  life 
materially.  Leaks  at  the  bottom  may  be  easily  tested 
for  by  blowing  into  the  top  of  the  globe.  Leaks  at  the 
top  of  the  globe  are  not  so  injurious  as  those  at  the 
bottom,  but  will  materially  reduce  the  life  of  the  carbon. 
They  may  be  caused  by  any  of  the  following  reasons:  a 
chipped  globe,  small  carbons,  worn  gas  cap  bushing,  gas 
caps  not  setting  squarely  against  the  globe,  or  warped 
gas  caps.  The  gas  cap  bushings  should  be  renewed  as 
soon  as  they  begin  to  show  signs  of  wear. 

Other  causes  which  may  produce  short  carbon  life  are: 

(a)  loose  dash  pots,  causing  the  lamp  to  jump; 

(b)  high    arc   voltage   or   any  condition   that   produces 
flaming; 

(c)  excessive  fluctuations  in  voltage  or  current; 

(d)  plugged  gas  check,   causing  direct  ventilation; 

(e)  frequent  starting  and  stopping  of  lamps; 

(f)  excessive  humiditV; 

(g)  the  lamp  subjected  to  strong  draught. 

Globes  have  been  founq  in  which  the  ground  edge§  were 

\       17 


not  perpendicular  to  the.  axis  of  the  globe.  This  may 
cause  the  carbons  to  bind  in  the  gas  cap. 

The  effect  of  rapid  burning  is  to  produce  points  on  the 
carbons  like  those  obtained  in  the  open  arc  lamp. 

The  globe  and  its  handling  has  more  effect  on  the  life 
of  the  trim  than  any  other  factor.  For  this  reason  the 
life  of  a  brand  of  carbons  should  not  be  judged  by  less 
than  ten  complete  burn-out  tests. 

POOR  LIGHT.  When  a  lamp  is  furnishing  poor  light 
the  trouble  may  lie  in  any  of  the  following  points: 

(a)  fresh  trim; 

(b)  low  voltage  or  current; 

(c)  lamp  not   lined  up,   causing  carbons  to   burn   with 
heavy    diagonal    faces    and    cast    heavy    shadow    to    one 
side; 

(d)  dirty  globe. 

Low  voltage  may  be  caused  by: 

(a)  low  line  voltage — this  will  affect  all  the  lamps  on 
the  circuit; 

(b)  improper  adjustment  of  lamp  mechanism  for  operat- 
ing conditions; 

(c)  carbon,  dash  pot  or  clutch  binding; 

(d)  failure  of  clutch  ring  or  tongue  to  grip  carbon; 

(e)  excessive  vibration  of  lamp,  causing  carbons  to  slip 
through   holder. 

GEAPHITIZATION.  Graphitization  is  caused  by  low 
line  voltage.  Graphitized  points  occur  in  any  interme- 
diate stage  between  soft,  greasy  graphite  and  hard,  lava- 
like  beads.  When  graphitization  occurs  with  cored  car- 
bons, the  cores  are  stopped  up  and  the  lamp  will  operate 
as  if  two  solid  carbons  were  being  used,  i.  e.,  it  will  jump 
badly.  If  these  points  are  broken  off,  the  lamp  will 
operate  properly  until  new  points  are  formed.  This 
trouble  is  very  apt  to  occur  in  the  D.  C.  lamp  if  the  arc 
voltage  falls  below  75  and  in  the  A.  C.  if  below  70.  With 
low  arc  voltage  the  clutch  operates  badly  and  allows  the 
carbon  to  slip,  causing  poor  burning  and  excessive  globe 

18 


deposit.  Small  or  flat  carbons  will  cause  graphitization 
with  normal  arc  voltage.  Graphitization  never  occurs  in 
lamps  operated  on  normal  voltage  with  carbons  of  the 
correct  size. 

JUMPING-.  Carbons  should  always  be  kept  dry.  Damp 
carbons  cause  the  lamp  to  jump  badly  when  the  current 
is  first  turned  on.  In  damp,  cored  carbons  steam  will 
be  formed,  which  is  liable  to  blow  out  the  coring  material 
and  give  the  same  effect  as  an  A.  C.  lamp  operating  with 
solid  carbons. 

Oil  and  grease  on  the  carbons  cause  the  lamp  to  jump 
badly  and  will  also  cause  globe  blackening.  Most  manu- 
facturers of  arc  lamps  direct  that  no  oil  should  be  used 
on  their  lamps  and  certainly  it  should  not  be  used  where 
there  is  any  danger  of  its  getting  on  the  carbons.  At  the 
present  time  most  lamps  use  graphite  dash  pot  plungers 
and  these  require  no  lubrication. 

If  the  dash  pot  plunger  is  too  loose  the  lamp  will  jump 
badly  when  it  is  first  turned  on,  but  it  will  soon  become 
quiet.  If  it  is  too  tight,  the  lamp  starts  quietly,  but  the 
arc  voltage  will  vary  considerably  and  the  arc  will  break 
more  or  less  frequently. 

Intermittent  jumping  may  be  caused  by  a  poor  -contact 
in  the  lamp  circuit.  To  locate  this  examine  the  lamp 
parts,  fuses,  switches,  etc.,  for  signs  of  heating  or  arcing. 

A.  C.  lamps  will  jump  badly  if  two  solid  carbons  are 
used. 

FLAMING.  Flaming  is  usually  caused  by  the  presence 
of  air  in  the  inner  globe.  It  is,  therefore,  likely  to  occur 
when  a  lamp  is  first  started.  In  A.  C.  lamps  it  may  be 
lessened  by  digging  out  the  core  of  the  new  cored  carbon 
for  about  %  inch. 

High  arc  voltage  will  cause  flaming.  This  large  power 
consumption  at  the  arc\  will  cause  excessive  heat,  which 
will  blacken  and  sometimes  even  melt  the  globe.  The 
product  of  the  arc  combustion  is  a  white  powder,  iron  sul- 
phate, which  is  deposited  on  the  gag  cap  and  top  of  the 

19 


globe.  The  intense  heat  of  the  arc  when  it  is  flaming 
converts  this  white  powder  to  a  brown  or  red  substance 
and  will  finally  burn  it  into  the  glass.  This  seriously  inter- 
feres with  the  light  of  the  arc. 

SLIPPING.  Worn  clutches  will  cause  the  carbons  to  slip 
badly.  In  such  cases  new  clutches  should  be  supplied. 

BUENED  OUT  SHUNT  COILS.  Burned  out  shunt  coils 
are  a  frequent  cause  of  trouble  in  series  arc  lamps.  If 
the  carbons  stick  and  the  cut-out  fails  to  work,  the 
current  through  the  shunt  coil  becomes  excessive  and  a 
burn-out  is  sure  to  result.  The  mechanism  may  wedge 
and  hold  the  contact  open  after  the  arc  has  broken  and 
the  same  thing  will  occur.  The  cut-out  contacts  should 
be  kept  in  good  condition  and,  if  burned  or  oxidized, 
should  be  cleaned  with  sand  paper.  If  there  is  improper 
adjustment,  it  may  cause  the  lamp  to  burn  with  an 
abnormally  long  arc.  This  causes  high  current  in  the 
shunt  coil,  but  usually  not  sufficient  to  cause  a  burn-out. 

In  the  multiple  arc  lamp,  improper  adjustment  may 
cause  overheating  and  possible  burning  out  of  the  series 
coils.  If  the  carbons  wedge  together  in  the  multiple 
lamp,  the  current  drawn  from  the  line  will  be  excessive 
and  the  regulating  resistance  will  be  burned  out  if  the 
fuse  does  not  blow.  This  high  current  may  damage  the 
insulation  of  the  series  coil. 

LAMP  ADJUSTMENT.  If  an  individual  lamp  gives 
short  life  for  several  trimmings,  it  is  probable  that  it  is 
out  of  adjustment  and  is  operating  at  a  high  arc  voltage. 
An  examination  of  the  carbons  will  usually  tell  if  this  is 
the  case,  high  arc  voltage  producing  pointed  carbons. 
The  lamp  should  be  readjusted  to  operate  at  the  correct 
arc  voltage  and  current.  For  this  work  an  ammeter  and 
a  voltmeter  are  necessary. 

It  is  advisable  to  test  and  to  properly  adjust  all  lamps 
for  actual  working  conditions  before  they  are  connected 
on  the  line.  All  lamps  are  thoroughly  tested  by  the  manu- 
facturer before  they  are  shipped,  but  the  conditions  under 

20 


factory  test  and  actual  operating  conditions  may  be 
decidedly  different. 

A  careful  inspection  should  also  be  made  before  the 
lamps  are  placed  in  service,  and  afterwards  at  regular 
intervals  to  see  that  no  screws  are  loose  and  that  all 
parts  are  in  good  condition.  There  is  a  continual  tendency, 
especially  in  the  A.  C.  lamp,  for  the  connections  to  become 
loose,  causing  arcing  and  throwing  the  lamp  out  of  adjust- 
ment. 

OPERATING  TROUBLES.  A  lamp  may  fail  to  start 
for  the  following  reasons: 

(a)  open   circuit,  external  or  internal; 

(b)  grounded  circuit; 

(c)  dash  pot  stuck; 

(d)  carbon  bound  in  trolley  tube,  clutch  or  gas  cap; 

(e)  joints  of  clutch  fail  to  work. 

When  trouble  occurs  with  a  lamp,  the  most  effective 
method  is  to  replace  it  and  send  the  defective  lamp  to 
the  shop  where  it  should  be  thoroughly  inspected  and 
repaired.  A  small  number  of  extra  lamps  should  always 
be  kept  in  stock  to  replace  the  lamps  under  repairs. 

A  lamp  should  never  be  kept  in  service  when  it  is 
not  operating  properly,  for  in  a  short  time  it  will  be 
ruined  and  in  the  meanwhile  will  give  unsatisfactory 
service. 

Eeeords  of  operation  and  repairs  should  always  be  kept 
on  suitable  blanks  to  be  filled  out  by  trimmers.  Such 
a  system  can  be  kept  with  little  expense  and  the  actual 
operating  conditions  noted. 

A  Few  Pointers 

Trim  lamps   regularly  and  carefully. 
See  that  lamps  are  adjusted  for  the  proper  voltage  and 
current. 

Keep  globes  and  gas  caps  clean. 
Use  high  grade  glassware. 
Use    COLUMBIA    carbons. 

21 


Flame  Arc  Lamps 

When  flame  arc  lamps  were  introduced  into  this  country 
several  years  ago,  they  were  considered  useful  only  for 
spectacular  advertising,  but  they  soon  proved  themselves 
to  be  practical  units  for  lighting  large  areas,  such  as 
streets,  parks,  or  industrial  plants,  their  immense  candle 
power  and  high  efficiency  allowing  a  much  higher  standard 
of  illumination  than  could  be  obtained  by  any  other 
means.  A  flame  arc  lamp  consuming  550  watts  will  pro- 
duce between  five  and  six  times  as  much  light  as  the 
ordinary  enclosed  arc  consuming  660  watts.  The  orange 
yellow  color  of  the  light  has  been  found  to  be  extremely 
well  suited  for  lighting  shops  and  railways  yards  where 
a  large  amount  of  smoke  is  liable  to  be  present  in  the 
air. 

Flame  lamps  may  be  divided  into  two  general  classes, 
the  inclined  carbon  lamp  in  which  both  carbons  are 
mounted  side  by  side  inclined  toward  each  other  at  an 
angle  of  about  30°  and  the  vertical  carbon  lamp  in  which 
one  carbon  is  superimposed  above  the  other  as  in  the 
ordinary  enclosed  arc.  The  first  is  probably  the  most 
popular  type. 

INCLINED  CARBON  LAMPS.  In  these  lamps  there 
are  three  distinctly  different  regulating  mechanisms  used, 
clock  feed,  motor  feed  and  gravity  feed.  In  the  clock 
feed  lamp  the  carbon  holders  are  suspended  by  chains  or 
flexible  wires  wound  on  a  drum.  The  downward  move- 
ment of  the  carbons  is  controlled  by  a  ratchet  operated  by 
shunt  and  series  coils.  This  mechanism  was  formerly 
used  on  D.  C.  lamps  only,  but  recently  several  manu- 
facturers have  applied  it  to  their  A.  C.  lamps.  The  motor 
feed  is  used  on  A.  C.  lamps  only.  The  carbons  are  sus- 
pended just  as  in  the  clock  feed  lamps.  The  drum  instead 
of  being  controlled  by  a  ratchet  has  an  aluminum  disc 
attached  to  it,  which  rotates  between  the  poles  of  shunt 


H 
D- 


K 


and  series  magnets.  The  gravity  feed  lamp  does  not 
employ  any  electrical  method  of  control  for  feeding  the 
carbons.  The  carbon  holders  are  rigidly  connected 
.  together  and  one  of  the  carbons  is  supported  at  its  lower 
end  on  a  projection  of  the  economizer  or  some  device 
attached  to  it.  The  carbons  are  fed  downward  as  they 
are  consumed.  To  steady  the  arc  and  hold  it  in  a  bowed 
position  at  the  ends  of  the  carbons,  a  magnetic  blow  down 
coil  connected  in  series  with  the  arc  is  used  in  most 
inclined  carbon  lamps. 

All  inclined  carbon  lamps  use  an  arch-shaped  porcelain 
plate  called  an  economizer.  The  carbons  pass  through 
holes  in  the  top  and  the  arc  is 
situated  directly  under  the  bowl: 
The  economizer  partly  encloses 
the  arc  and  reduces  the  con- 
sumption of  the  carbons.  It 
soon  becomes  covered  with  a 
white  ash  deposit  and  serves  as 
an  excellent  reflector.  It  also 
protects  the  arc  from  draughts 
and  thus  greatly  improves  the 
burning  qualities. 

A  clock  feed  lamp  with  its 
casing  removed  is  shown  in 
Fig.  7.  H  is  the  series  and  K 
the  shunt  coil  operating  the 
armature  E,  which  controls  the 
drum  supporting  the  carbons. 
Eaising  the  armature  releases 
the  ratchet  and  allows  the 
carbons  to  feed  downward. 
When  the  lamp  is  first  turned 
on,  the  carbons  are  separated 
and  no  current  can  flow  through 
the  series  coil.  The  shunt  coil, 


FiS- 


however,  is  excited  and  pulls  up  the  armature,  allowing 


the  carbons  to  feed  downward.  At  the  same  time,  a  shoe, 
situated  on  the  top  of  the  economizer  and  operated  from 
the  armature  E  by  a  rod  at  the  back  of  the  lamp,  pushes 
f  ^  ~*J  over  the  right  hand  carbon 

until  it  touches  the  left,  clos- 
ing the  circuit  through  the 
lamp.  Current  then  passes 
through  the  series  coil  pulling 
down  the  armature.  This  stops 
the  feed  and  removes  the  shoe, 
allowing  the  right  carbon  to 
fall  back  to  its  position  to 
form  the  arc.  As  the  carbons 
are  consumed,  the  strength  of 
the  shunt  coil  increases  and 
the  carbons  are  fed  downward. 
This  increases  the  strength  of 
the  series  coil  which  stops  the 
feeding.  The  dash  pot  D  is 
used  to  steady  the  movement 
of  the  armature.  R  is  the 
regulating  resistance  to  cut 
down  the  line  voltage  to  that 
of  the  arc.  B  is  the  blow  down 
coil  in  series  with  the  arc. 

Fig.  8  shows  another  clock 
feed  lamp  of  different  con- 
struction. The  carbon  holders 
C  and  C'  are  rigidly  connected 
together  and  supported  on  the 
vertical  rod  B.  This  rod  has  a 
spiral  groove  cut  into  its  side 
Fig.  8.  and  as  this  rod  turns  the  car- 

bons  are   fed   downward.     The   rod   is   controlled  by   the 
series  coil  H  and  a  shunt  coil  K  at  the  back  of  the  lamp. 
R  is  the  regulating  resistance  and  D  the  dash  pot. 
Fig.  9  shows  the  mechanism  of  a  motor  feed  lamp.    The 


aluminum  disc  D  is  connected  to  the  shaft  of  the  drum  on 
which  the  chains  supporting  the  carbon  holders  C  and 
C'  are  wound.  This  disc  rotates  between  the  poles  of  the 

series  magnet  H 

and    the    shunt 

magnet  K.    The 

current  induced 

in   the  disc  by 

the  series  mag- 

n    e    t      rotates 

the      drum      in 

the  direction  to 

raise    the     car- 

b  o  n  s,       while 

that  induced  by 

the  shunt  tends 

to   rotate   it   in 

the        other 

direction  low- 
ering them. 

When  the  lamp 

is      turned      on 

the  shunt  mag- 
net is  excited 

and  the  car- 
bons are  lower- 
ed until  they 

touch.     Current 

then       fl  o  w  s 

through      the 


Fig.    9. 


Fig.    10. 


series  coil  which  raises  the  carbons  forming  the  arc.  As 
the  carbons  are  separated  the  strength  of  the  series  coil 
decreases,  while  that  of  the  shunt  increases  until  when 
they  are  of  the  same  strength  the  disc  is  held  in 
equilibrium.  As  the  carbons  are  consumed  the  arc  volt- 
age increases  and  the  shunt  coil  becomes  the  stronger  and 
lowers  the  carbons.  R  is  the  regulating  resistance  and  B 
the  blow  down  coil.  This  type  of  lamp  uses  no  dash  pot, 
the  magnetic  forces  on  the  disc  acting  as  dampers. 

The   mechanism   of  a  gravity  feed  lamp   is  shown   in 
Fig.  10.    The  carbons  are  supported  by  a  projection  on  the 


economizer  and  are  fed  downward  as  the  carbon  resting  on 
the  support  is  burned  away.  The  carbons  are  held  apart 
by  the  series  coil  operating  the  rod  and,  as  soon  as  the 
current  ceases  to  flow  through  this  coil,  the  unsupported 
carbon  falls  into  contact  with  the  other.  The  carbon 
holders  are  rigidly  connected  together  and  slide  on  the 
center  vertical  rod.  When  the  lamp  is  switched  on,  the 
carbons  are  in  contact  and  the  current  flowing  through 
the  series  coil  separates  the  carbons  and  forms  the  arc. 
This  lamp  burns  one  round  carbon.  The  other  has  a  rib, 
which  rests  on  the  support. 

Many  attempts  have  been  made  to  increase  the  burn- 
ing period  of  flame  lamps  by  the  use  of  more  than  one 
pair  of  carbons.  These  are  usually  called  magazine  lamps. 
One  type  uses  two  pair  of  carbons,  the  second  pair  being 
switched  into  the  circuit  after  the  first  is  consumed.  In 
another  type  the  carbons  are  burned  alternately,  the  arc 
changing  from  one  pair  to  another  every  few  minutes. 
As  many  as  eight  or  ten  pairs  of  carbons  are  used  in 
some  lamps.  The  carbons  are  usually  held  in  a  vertical 
rack  or  magazine. 

One  of  the  recent  forms  of  magazine  lamps  uses  two 
pairs  of  flat  carbons  with  bridged  cores,  as  shown  in 
Pig.  11.  The  two  carbons  of  the  same  polarity  are 

inclined  toward  each  other 
I  and  touch  at  their  lower 
ends,  thus  supporting  them- 
selves, and  feeding  down- 
ward by  gravity  as  they  are 
I  consumed.  While  the  lamp 
is  in  service  the  positive  and 
negative  electrodes  are  held 
apart  by  magnet  coils  at  the  top  of  the  lamp.  When  these 
coils  are  not  energized  all  four  carbons  are  in  contact. 
The  arc  wanders  across  the  ends  of  the  carbons  consum- 
ing them  evenly.  This  lamp  may  be  procured  to  give 
burning  periods  up  to  100  hours. 


VERTICAL  CARBON  LAMPS,  in  a  way,  are  nothing 
but  modifications  of  the  open  and  enclosed  arcs  burning 
flaming  carbons.  In  most  cases  the  regulating  mechanism 
is  very  similar  to  that  of  the  multiple  enclosed  arc  lamp 
already  described.  In  most  cases  no  economizer  is  used, 
but  one  of  the  well  known  types  uses  an  economizer  with 
a  focusing  arc,  i.  e.,  both  carbons  are  fed,  the  upper  one 
downward  and  the  lower  one  upward,  in  this  way  keep- 
ing the  arc  directly  below  the  bowl  of  the  economizer. 
This  lamp  uses  a  clock-work  feed. 

Another  form,  called  the 
regenerative  fl  a  m  e  arc 
lamp,  is  an  enclosed  lamp 
with  suitable  condensing 
tubes  at  the  sides  to  col- 
lect the  mineral  fumes 
from  the  arc  and  prevent 
their  deposit  on  the  inner 
globe.  The  arc  chambers 
and  condensing  tubes  are 
shown  in  Fig.  12.  The  heat 
of  the  arc  causes  a  circu^ 
lation  of  the  gases  through 
the  tubes  as  indicated  by 
the  arrows.  Condensation 
takes  place  on  the 
cooler  walls  of  the 
tubes.  The  inner 
globes  and  tubes  are  prac- 
tically air-tight,  so  a  long 
burning  period  of  from  60 
to  70  hours  is  obtained. 
This  lamp  uses  a  star- 
shaped  lower  carbon,  open- 
ings between  the  ribs  being 
filled  with  flaming  material. 


12. 


The  upper  carbon  is  round,  with  six  small  cores  contain- 
ing flaming  material.  In  the  D.  0.  lamp  the  lower  carbon 
should  be  positive. 

The  distribution  of  the  light  given  by  the  inclined  car- 
bon and  the  vertical  trim  lamps  is  shown  in  Fig.  13  by 
the  curves  A  and  B.  The  inclined  carbon  gives  its  maxi- 
mum intensity  directly  downward,  as  shown  by  A,  so  that 
to  properly  illuminate  a  large  area,  it  is  necessary  that 
the  lamps  be  hung  high.  One  company  manufacturing 
inclined  carbon  lamps  uses  an  inner  prismatic  globe  to 
improve  the  distribution,  as  shown  in  curve  C.  The 
vertical  carbon  lamp  gives  a  distribution  with  its  maxi- 


mum  intensity  15° — 20°  below  the  horizontal  (curve  B). 
This  kind  of  a  distribution  curve  is  more  suitable  for 
street  lighting  than  the  other  because  it  throws  out  more 
of  its  light  toward  the  point  of  minimum  illumination, 
i.  e.,  half  way  between  the  lamps,  consequently  the 
difference  between  maximum  and  minimum  illumination 
will  not  be  so  great. 


Operation  and  Care  of  Flame  Arc  Lamps 

Flame  arc  lamps  are  made  for  operation  on  both  direct 
and  alternating  current  circuits.  They  are  usually  con- 
nected two  in  series  across  110  or  four  in  series  across 
220  volt  circuits.  However,  there  are  lamps  on  the 
market  which  may  be  connected  three  in  series  across 
110  volt  circuits  and  others  which  may  be  placed  directly 
across  110  volts.  A.  C.  lamps  are  sometimes  operated 
from  constant  potential  circuits  of  110  to  550  volts 
through  a  compensator  or  transformer  hung  directly  above 
the  lamp.  In  most  cases  the  lamps  connected  in  series 
multiple  are  not  provided  with  a  compensating  resistance, 
so  if  one  lamp  goes  out,  the  others  in  series  with  it  go 
out  also. 

A.  C.  flame  lamps  may  be  operated  on  circuits  of  any 
frequency  from  25  to  140  cycles. 

ARC  VOLTAGE.  The  arc  voltage  of  most  of  the 
inclined  carbon  lamps  varies  between  42  and  48.  If  it 
falls  below  40  the  lamp  is  liable  to  flicker,  or  rises  over 
50  the  carbons  will  be  consumed  too  rapidly  and  the 
lamp  does  not  burn  steadily.  The  arc  voltage  of  the 
vertical  carbon  lamp  varies  widely  with  the  form  of 
lamp.  One  type  uses  arc  voltage  of  38-42,  while  the  regen- 
erative type  burns  with  68-72  volts  across  the  arc.  It  is 
most  important  that  a  lamp  should  burn  with  the  correct 
value  of  arc  voltage  as  specified  by  the  manufacturer. 
A  high  arc  voltage  will  cause  rapid  consumption  of  the 
carbons  and  consequent  decrease  in  burning  period.  A 
low  arc  voltage  will  cause  a  weak  light. 

CARBONS.  Only  the  very  highest  grade  of  carbons 
should  be  used.  They  should  be  straight,  have  a  smooth 
surface,  and  be  of  uniform  diameter  and  composition. 
SILVEETIP  CARBONS,  manufactured  exclusively  by  the 
National  Carbon  Company,  satisfy  all  the  demands  of 
the  flame  lamp.  They  are  made  of  the  highest  grade  of 
materials  and  are  accurately  gauged,  both  for  size  and 

29 


straightness.  In  addition,  they  have  that  important 
mechanical  feature — the  Silver  Tip — which  does  away 
with  the  loose  end  of  wire  found  in  other  flame  carbons. 
This  makes  trimming  easy  and  always  insures  a  good 
contact  between  the  carbon  and  holder.  Another  impor- 
tant advantage  of  the  SILVERTIP  is  that  there  is  no 
necessity  of  throwing  away  any  carbons  because  of 
broken  wires. 

The,  carbons  should  be  kept  dry;  damp  carbons  cause 
the  lamp  to  flicker  badly  and  the  steam  formed  when  the 
lamp  is  turned  on  is  liable  to  blow  out  the  cores. 

When  trimming  a  flame  arc  lamp  with  carbons  contain- 
ing metallic  cores,  care  should  be  taken  that  the  wires 
in  the  carbons  are  placed  on  the  side  away  from  the 
ajc,  otherwise  the  arc  will  operate  badly  and  cause 
flickering. 

When  the  carbon  holders  are  rigidly  connected,  as  in 
the  gravity  feed  and  some  clock  feed  lamps,  it  is  extreme- 
ly important  that  the  carbons  should  be  exactly  the  same 
length.  Otherwise,  the  longer  carbon  must  be  cut  off 
before  inserting  it  into  the  lamp. 

In  most  cases  the  A.  G.  lamp  uses  carbons  of  the  same 
size,  but  the  D.  C.  takes  a  slightly  larger  positive  than 
negative. 

D.  C.  lamps  must  always  be  connected  to  the  line  with 
the  polarity  correct,  otherwise  they  will  burn  with  a  weak 
white  light  and  the  carbons  will  be  consumed  unevenly. 
Any  lamps  connected  in  series  will  also  be  affected  and 
burn  unsteadily.  The  polarity  can  be  found  by  allowing 
the  lamp  to  burn  a  few  minutes  and  then  turning  it  off, 
the  hotter  carbon  is  the  positive.  The  positive  carbon 
has  a  larger  incandescent  area.  The  terminals  of  most 
D.  C.  lamps  are  marked  P  or  N  for  positive  or  negative. 
In  the  vertical  carbon  lamps  the  positive  carbon  should 
be  the  lower,  which  is  the  reverse  of  enclosed  arc  practice. 

Most  inclined  carbon  lamps  are  made  in  two  sizes, 
the  ten-hour  lamp  burning  carbons  400  mm.  long  and  the 

30 


seventeen-hour  lamp  burning  carbons  600  mm.  long.  There 
is  a  twenty-hour  lamp  on  the  market  burning  carbons 
650  mm.  long. 

The  color  of  the  light  of  the  flame  arc  depends  on  the 
chemicals  with  which  the  carbons  are  impregnated.  The 
yellow  light  is  usually  the  most  efficient  and  for  that 
reason  is  most  widely  used.  The  red  is  next,  giving  an 
efficiency  of  10  to  20  per  cent,  lower  than  that  of  the 
yellow,  while  the  white  is  still  lower — 25  to  40  per  cent, 
lower  than  the  yellow. 

STRIKING-  POINT.  To  obtain  a  long  life  from  flame 
arc  carbons  the  arc  should  always  burn  within  the  bowl 
of  the  economizer.  To  obtain  this  the  carbons  must  have 
the  correct  striking  point.  For  adjusting  this,  the  lamp 
manufacturers  furnish  steel  rods  with  squared  ends  of 
the  exact  size  of  the 
carbons.  These  are 
placed  in  the  lamp 
and  fed  downward 
until  they  touch. 
This  position  for 
clock  feed  lamps 
should  be  in  line- 
with  the  lower  edge 
of  the  economizer, 
as  shown  in  Fig.  14. 
For  the  motor  feed  lamps  the  striking  point  should  be 
%  inches  below  the  lower  edge  of  the  economizer,  as  in 
Fig.  15.  If  the  rods  are  not  available,  carbons  whose 
ends  have  been  squared  with  a  file  may  be  used.  When 
the  lamps  operate  poorly  and  whenever  new  lamp  parts 
are  supplied,  the  striking  point  should  be  adjusted. 

BURNED-OUT  ECONOMIZERS.  If  the  arc  is  allowed 
to  burn  too  near  the  top  of  the  economizer,  or  with  too 
high  an  arc  voltage,  the  economizer  is  liable  to  be  burned 
out.  This  trouble  may  also  occur  if  both  carbons  stick 
and  the  arc  travels  up  the  carbons. 

31 


SLIPPING.  Trouble  is  sometimes  experienced  due  to 
carbons  slipping.  This  may  be  caused  by  some  part  of 
the  lamp  mechanism  sticking  or  by  projections  on  the 
carbon.  Care  should  be  taken  to  see  that  the  carbons 
are  smooth  before  inserting  them  in  the  lamp.  When 
one  carbon  hangs,  the  other  will  be  fed  downward  to  the 
end  of  its  travel  and  if  it  is  long  enough  to  strike  the 
ash  pan,  it  will  connect  one  side  of  the  line  to  the  frame 
of  the  lamp.  This  may  develop  a  short  circuit  at  some 
weak  spot  in  the  lamp.  This  trouble  could  only  occur 
in  lamps  using  independent  carbon  holders. 

CLEANING.  At  each  retrimming,  the  globe  equipment 
and  all  lamp  parts  on  which  the  products  of  combustion 
have  condensed  should  be  cleaned  thoroughly  with  a 
brush  or  with  a  dry  cloth.  The  condensing  tubes  of  the 
regenerative  lamp  should  be  cleaned  with  a  brush.  The 
manufacturers  give  the  following  rules  for  cleaning: 
Insert  the  brush  into  the  lower  opening  of  the  regenera- 
tive chamber;  the  brush  can  then  be  passed  up  into  both 
tubes  and  also  through  the  globe,  taking  special  care  to 
clean  deposit  from  the  portion  over  the  globe,  and  leave 
the  tubes  unobstructed.  Obstruction  in  the  tubes  will 
prevent  the  lamp  burning.  Before  inserting  the  lower 
cone  holder,  care  should  be  taken  to  clean  off  all  traces 
of  white  powder  from  the  cone  surface,  both  on  the  lamp 
frame  and  holder.  An  occasional  application  of  graphite 
will  entirely  prevent  sticking  of  the  cone  in  its  seating. 
Deposit  in  the  outer  globe  is  caused  by  the  inner  globe 
cap  not  seating  tightly  upon  the  inner  globe. 

With  the  regenerative  lamp,  care  should  be  taken  in 
seating  the  globes  properly  as  it  is  necessary  to  secure 
air-tight  joints  in  order  to  obtain  a  maximum  life  from 
the  carbons. 

Heavy  globe  deposit  will  cause  a  decided  decrease  in 
the  light. 

Flickering  may  be  caused  by  wet  or  greasy  carbons, 
or  by  a  wet  globe. 

32 


Jumping  is  caused  by  high  arc  voltage  and  by  damp  or 
greasy  carbons.  Intermittent  jumping  may  be  caused  by 
a  loose  connection  in  the  circuit. 

One  of  the  large  manufacturers  of  flame  arc  lamps  gives 
the  following  rules  for  operation.  If  lamp  fails  to  operate 
satisfactorily,  open  case  and  carefully  inspect  the  follow- 
ing parts: 

Dashpot — Must  be  quite  clean  and  plunger  slide  easily 
in  same;  if  it  does  not,  wipe  carefully  with  clean  cloth. 
On  no  account  use  ordinary  emery  paper  or  oil  in  the 
dashpot.  Examine  the  screws  holding  the  dashpot  to 
its  seat  and  see  if  they  are  tight  and  hold  the  dashpot 
firmly. 

Armature — See  if  this  works  smoothly  and  freely  with- 
in the  solenoid  tube  throughout  its  range  of  motion.  If 
necessary,  clean  the  inside  of  solenoid  tube  with  a  clean 
cloth. 

Upper  Holder — See  that  the  slotted  end  of  the  holder 
grips  the  carbon  firmly.  Be  sure  that  the  carbon  requires 
a  perceptible  pull  to  come  out  of  holder,  or  it  may  drop 
out  accidentally  and  short-circuit  the  lamp.  Use  a  full 
length  carbon,  pushing  it  upwards  to  its  full  movement, 
and  allowing  it  to  fall  by  its  own  weight,  with;  fingers 
supporting  it.  This  will  show  that  it  is  free  from  friction 
and  all  danger  of  binding  or  sticking  when  lamp  is  burn- 
ing. 

Clutch — See  that  this  rises  smoothly  on  its  guide  rod. 
Note  that  it  grips  carbon  promptly  and  firmly,  and  that 
the  carbon  when  gripped  by  clutch  cannot  slip  through, 
even  when  pulled  downwards  by  hand.  Try  if  the  clutch 
is  easily  released  by  the  weight  of  the  mechanism;  the 
mechanism  when  moving  as  slowly  as  possible  (guide  this 
with  a  finger)  should  be  able  to  press  the  clutch  flat  on 
its  seat.  Chips  off  upper  carbon  will  sometimes  collect 
under  clutch  and  should  be  removed. 


33 


TABLE    1 

Light  Reflected  by  Various  Colors 

Per    Cent. 

White   blotting   paper    82 

White  cartridge  paper   80 

Ordinary  foolscap    70 

Ordinary  newspaper    50  to  70 

Chrome  yellow  paper    62 

Orange  paper    50 

Plain  boards,  clean   45 

Plain  boards,  dirty   20 

Yellow   wall   paper    40 

Light  pink ! 36 

Blue 25 

Yellow   painted   wall,   clean 40 

Yellow  painted  wall,   dirty 20 

Emerald  green  paper    18 

Dark  brown 13 

Vermilion    12 

Blue-green     12 

Cobalt  blue • 12 

Black    0.5 

Deep   chocolate    0.4 

French    ultramarine    3.5 

Black    cloth    1.2 

Black   velvet    0.4 

Table  shows  how  important  it  is  to  have  light  colored 
walls  and  ceilings. 

TABLE  2 

Interior  Illumination 

The    desirable    intensity    of    illumination    for    various 
classes  of  interior  service  has  been  given  as  follows: 

Auditoriums    1  to    3  ft.  candles 

Theatres    1  to    3ft. 

Churches    3  to    4  ft. 

Beading    1  to    3  ft. 

Eesidences    (General)    1  to    2  ft. 

Desks    , 2  to    5  ft. 

Bookkeeping    3  to    5  ft. 

Postal  service    2  to    5  ft. 

Stores    (General)    2  to    5  ft. 

Stores    (Clothing)    4  to    7ft. 

Drafting    .5  to  10  ft. 

Engraving    5  to  10  ft. 

34 


fl.C    SUPPLY 

IA/VWWWV\! 


Station  Equipment 

Multiple  arc  lamps  require  no  special  equipment,  but 
are  connected  directly  across  incandescent  lighting  or 
power  circuits. 

The  series  lamps,  however,  require  special  apparatus  to 
hold  the  line  current  at  a  constant  value  at  all  times, 
no  matter  how  many  lamps  are  cut  out  of  the  circuit. 
Series  lamps  may  be  operated  on  either  D.  C.  or  A.  C., 
but  at  the  present  time  very  few  D.  C.  series  carbon  lamps 
are  being  installed. 

CONSTANT  CURRENT  APPARATUS.  Constant  cur- 
rent D.  C.  may  be  supplied  by  a  special  arc  dynamo,  or 
from  a  mercury  arc  rectifier.  These 
dynamos  are  series  wound  and,  in 
most  cases,  use  a  solenoid  regulator 
connected  in  series  with  the  line  for 
controlling  the  current.  In  one  type 
of  machine  the  brushes  are  shifted 
on  the  commutator,  increasing  or 
decreasing  the  line  voltage  as  may 
be  necessary.  In  another,  a  resist- 
ance is  shunted  across  the  field 
winding.  By  varying  this  resistance 
the  strength  of  the  field  and  con- 
sequently the  voltage  of  the  machine 
is  varied.  The  armatures  are  some- 
times made  with  several  independent 
windings  for  supplying  separate 
lamp  circuits.  The  voltage  that  can 
be  obtained  from  each  of  these  cir- 
cuits is  3000  to  5000  and  usually 
about  50  enclosed  lamps  are  connected  in  series  on  a 
single  circuit. 

A  mercury  arc  rectifier  is  sometimes  used  to  obtain  con- 
stant current.  It  is  connected  on  the  secondary  winding 

35 


of  a  constant  current  transformer,  which  will  be  described 
later.  The  transformer  supplies  constant  current  A.  C.  to 
the  rectifier,  which  delivers 
constant  current  D.  C.  to  the 
line.  These  elementary  con- 
nections are  shown  in  Fig.  16. 
For  obtaining  constant  cur- 
rent A.  C.  a  special  trans- 
former, or  a  choke  coil  regu- 
lator, is  used.  The  operation 
of  the  transformer  depends  on 
the  fact  that  the  current 
induced  in  a  secondary  coil  by 
a  primary  varies  inversely  as 
the  distance  between  the  two 
coils;  that  is,  as  this  distance 
increases,  the  current  induced 
decreases. 

A  constant  current  transformer  is  shown  in  Fig.  17. 
It  consists  of  a  laminated  iron  core  C  around  which  the 
stationary  coil  A  is  placed.  Above  A  suspended  from 
the  pivoted  lever  I)  is  the  movable  coil  B.  The  weight 
of  the  coil  is  counterbalanced  by  the  adjustable  weight  G. 
The  currents  in  the  primary  and  secondary  coils  cause 
them  to  repel  each  other  so  that  by  properly  adjusting 
the  weight  G  the  secondary  may  be  regulated  to  give  the 
desired  current.  When  the  current  exceeds  this  value  the 
coils  will  be  separated  further,  reducing  the  current  to 
its  proper  value.  The  movable  coil  is  usually  the  second- 
ary and  the  stationary  the  primary.  These  transformers 
are  made  in  sizes  up  to  100  lamps  on  a  single  circuit.  On 
the  larger  sizes,  one  type  has  two  primary  and  two 
secondary  coils,  the  primaries  usually  being  fixed  at  the 
top  and  bottom,  while  the  secondaries  move  between  them. 
In  this  case  the  counterbalance  mentioned  above  is  con- 


36 


VVWVWVV1 


fi^.18. 

VWWWV\/VJ 


siderably   smaller.     In   the   first   case   the   counterbalance 

is  equal  to  the  weight  of  the  moving  coil  less  the  electrical 

repulsion,  while  in  the  second  case  the  two  moving  coils 

are  balanced  against  each  other,  and  the  counter-weight 

simply     balances     the     repulsive 

force.       Therefore,    in    adjusting  ^p] 

these  transformers  the  current  is  Q 

increased      by      decreasing      the 

counter-weight  in  the  small  sizes, 

and     by     increasing     it     in     the 

larger   sizes.     In  another  type  a 

single   primary   coil   is   placed   in 

the    center    of    the    core    with    a 

secondary  coil  suspended  on  each 

side.     A  separate  weight  is  used 

to  counterbalance  each  secondary 

coil. 

Most  constant  current  trans- 
formers are  air-cooled,  and  a  dash 
pot  is  supplied  to  prevent  the 
moving  coil  from  see-sawing 
every  time  a  variation  in  cur- 
rent occurs.  If  this  oscillation 

were  not  checked,  the  lamps  on  the  circuit  would  flicker. 
Some  transformers  are  oil-cooled,  and  in  these  the  dash 
pot  is  not  necessary  as  the  resistance  which  the  oil  offers 
to  the  motion  of  the  coil  is  sufficient  to  prevent  flickering. 

A  simple  wiring  diagram  for  a  constant  current  trans- 
former and  the  necessary  instruments  is  shown  in  Fig.  18. 

When  switching  on  a  lamp  circuit  using  a  constant  cur- 
rent transformer,  the  movable  coil  should  be  raised  to  its 
highest  position  before  the  switch  is  closed  to  avoid 
the  heavy  flow  of  current  caused  by  the  carbons  of  all 
the  lamps  being  in  contact.  Where  there  are  two  mov- 
able coils,  these  should  be  in  the  central  position  when 


37 


starting,  that  is  as  far  away  from  the  stationary  coils  as 
possible. 

Instead  of  a  transformer  a  single  coil  regulator  or  choke 
coil  is  sometimes  used.  When  an  alternating  current 
passes  through  a  coil  of  wire,  it  reacts  on  itself  and  a 
counter  e.  m.  f.  is  induced,  which  opposes  the  flow  of  the 
current.  This  counter  e.  m.  f.  is  greatly  increased  by 
inserting  an  iron  core  in  the  coil. 

One  type  regulator  operates  on  this  principle.  It  con- 
sists of  a  movable  coil  A  (Fig.  19)  connected  in  series 
with  the  lamps.  It  is  sus- 
pended and  counterbalanced 
just  as  the  movable  coil  in  the 
transformer.  When  the  cur- 
rent rises  above  the  desired 
value,  it  strengthens  the  mag- 
netic effect  of  the  coil  and 
pulls  it  up  further  into  the 
core.  This  increases  the  chok- 
ing effect  of  the  coil  and  the 
current  is  reduced.  A  dash 
pot  is  usually  provided  to 
steady  the  movement  of  the 
coil.  This  dash  pot  is  objec- 
tionable for  small  variations, 
but  is  desirable  when  a  large  movement  of  the  coil  is 
necessary,  as  when  several  lamps  cut  out  at  the  same 
time.  This  difficulty  is  overcome  in  one  type  of  regulator 
by  supplying  a  dash  pot  with  a  certain  amount  of  lost 
motion.  In  another  type  of  regulator  the  coil  and  core 
are  both  movable,  and  suspended  in  such  a  way  as  to 
counterbalance  each  other. 

The  elementary  wiring  diagram  for  a  regulator  is 
shown  in  Fig.  20.  A  step-up  transformer  is  used  between 
the  supply  circuit  and  the  lamps.  This  is  not  necessary 


38 


when  the  supply  circuit  is 
of  the  proper  voltage,  but  it 
is  always  advisable  to  use 
the  transformer  no  matter 
what  the  supply  voltage 
may  be  as  it  separates  the 
arc  lamp  circuits  from  the 
supply  mains.  This  trans- 
former should  preferably 
be  supplied  with  taps  to 
give  various  voltages,  so 
that  the  number  of  lamps 
installed  may  be  changed  at 
any  time  without  decreas- 
ing the  efficiency  of  the 
system. 

When  starting  an  arc 
lamp  circuit  using  a  regu- 
lator, care  should  be  taken 
that  the  regulator  is  in  the 
"no  load"  position  before 
the  switch  is  closed.  In 
some  regulators  a  latch  is  provided  to  hold  the  coil  in  this 
position.  After  the  current  is  turned  on,  the  latch  should 
be  loosened  and  the  regulator  slowly  moved  to  the  run- 
ning position.  In  another  regulator,  a  reactance  coil  is 
connected  directly  across  the  lamp  circuit  through  the 
lower  terminals  of  the  starting  switch.  When  the  cur- 
rent is  turned  on,  the  line  is  short-circuited  through  this 
reactance  coil  and  the  regulator  moves  to  its  no-load 
position.  The  starting  switch  should  now  be  closed.  This 
short-circuits  the  reactance  coil  and  opens  the  circuit 
across  the  line. 

The  switchboards  used  for  series  arc  lamp  circuits  are 
of  a  distinct  type.  It  is  sometimes  advisable,  in  cases 
where  a  number  of  arc  lamp  circuits  are  used,  to  be  able 
to  connect  a  transformer  on  any  one  of  several  circuits 


and  to  have  several  transformers  available  for  each  cir- 
cuit. This  is  accomplished  by  using  two  sets  of  bus  bars. 
The  transformers  are  connected  to  a  vertical  set,  while 
the  lamp  circuits  go  to  the  horizontal.  Plug  switches  are 
provided  where  the  bars  cross  to  connect  any  transformer 
to  any  lamp  circuit.  The  wiring  for  a  switchboard  for 
three  lamp  circuits  is  shown  in  Fig.  21.  The  black  circles 


k™£ 


show  where  the  plug  switches  are  inserted,  while  the  light 
ones  indicate  the  position  of  the  other  switches.  The 
vertical  bars  at  the  right  of  the  diagram  are  not  con- 
nected to  any  transformer,  but  are  used  for  inter- 
connecting circuits  in  various  ways.  For  instance,  in  the 
diagram  as  shown,  circuits  1  and  2  are  both  connected 
in  series  to  transformer  1,  while  circuit  3  is  connected 
to  transformer  3. 

It  is  advisable,  but  not  necessary,  to  use  a  current 
transformer  for  the  ammeter  in  the  lamp  circuit.  It 
should  always  be  done  in  circuits  of  over  35  lamps. 

It  is  customary  to  use  a  voltmeter  and  wattmeter  in 
the  primary  circuit  of  the  transformer. 

All  outgoing  lines  should  be  protected  with  lightning 
arresters, 


Line  Work 

For  outside  series  arc  lamp  circuits  weatherproof  wire 
should  be  used.  The  line  should  be  designed  not  only 
for  carrying  capacity,  but  should  have  sunicient  tensile 
strength  to  withstand  a  high  wind  when  the  wire  is 
covered  with  ice. 

The  voltage  of  the  circuit  is  high,  so  care  should  be 
taken  to  insulate  it  properly  and  allow  sufficient 
clearances. 

Outside  lamps  may  be  suspended  in  three  ways: 
1,  placed  on  the  top  of  the  pole;  2,  suspended  from  brackets 
at  the  side  of  the  pole  or  building;  3,  suspended  on  a 
wire  stretched  across  the  street.  The  first  method  does 
not  allow  the  lamp  to  be  lowered  and  steps  must  be  pro- 
vided to  allow  the  trimmer  to  climb  the  pole.  The 
second  and  third  methods  are  practically  the  same,  in  one 
case  the  lamp  is  suspended  from  an  arm  on  the  pole  and 
in  the  other  from  a  steel  cable.  In  both  cases  the  lamp 
is  arranged  to  be  lowered  to  the  street.  A  y2  inch  or 
%  inch  hemp  or  cotton  rope  is  used  to  raise  and  lower 
the  lamp.  A  flexible  wire  or  chain  may  be  used,  but  it 
should  always  contain  a  strain  insulator  for  the  trimmer's 
protection.  Enough  rope  may  be  provided  to  allow  the 
lamp  to  be  lowered,  or  it  may  be  cut  short  and  have  a 
loop  in  the  end,  in  which  case  the  trimmer  carries  a  short 
rope  which  he  hooks  to  the  end  of  the  lamp  rope  when 
the  lamp  is  being  lowered. 

The  pulley  should  be  provided  with  a  clutch  which  will 
support  the  lamp  in  case  the  rope  breaks  or  becomes 
untied.  Pulleys  with  hoods  to  protect  them  from  snow 
and  sleet  should  be  used. 

A  short  cross-arm  insulator  should  be  fastened  directly 
above  the  lamp  to  which  the  wires  are  connected. 

Each  multiple  lamp  should  be  provided  with  a  suitable 

41 


fuse  to  protect  it  from  being  burned  out  and  to  protect 
the  other  lamps  on  this  line  from  disturbances  due  to  a 
single  lamp. 

The  height  a  lamp  should  be  hung  above  the  street 
depends  on  local  conditions.  In  open  streets  where  there 
are  no  trees  to  interfere  lamps  may  be  hung  fairly  high — 
25  to  30  feet.  In  shaded  streets  this  should  be  less. 

For  inside  work  the  wire  for  series  arc  lamp  circuits 
should  have  approved  rubber  covered  insulation. 

The  wires  should  be  arranged  to  enter  and  leave  the 
building  through  an  approved  double  contact  service 
switch  mounted  in  a  non-combustible  case  free  from 
moisture  and  easily  accessible  in  case  of  fire  or  other 
emergency.  By  a  double  contact  switch  is  meant  one 
which  first  short-circuits  the  loop  and  then  disconnects  it 
from  the  main  circuit. 

The  wires  should  be  in  plain  sight  and  never  encased 
except  when  required  by  the  inspection  department. 

The  insulators  supporting  the  wires  should  separate 
them  at  least  1  inch  from  the  surface  wired  over.  The 
wires  should  be  held  rigidly  at  least  8  inches  from 
each  other. 

Lamps  should  be  hung  from  insulated  supports  other 
than  their  conductors. 


42 


Locating  Troubles 
on  Series  Arc  Lamp  Circuits 

The  three  chief  causes  of  trouble  which  may  occur  on 
series  arc  lamp  circuits  are  breaks,  grounds  and  crosses. 
When  the  whole  wire  is  broken  the  trouble  can  easily 
be  detected,  but  it  frequently  happens  that  the  conductor 
breaks  and  the  insulation  supports  the  wire,  giving  no 
visible  indication  of  trouble.  This  is  liable  to  occur  where 
the  wire  is  dead  ended  to  the  insulator  at  the  lamp. 
Grounds  are  of  two  kinds.  The  dead  ground  in  which 
the  circuit  has  permanent  connection  to  the  earth;  and 
the  arcing  ground,  such  as  is  caused  by  the  wet  branch 
of  a  tree  being  blown  against  the  wire  where  the  insula- 
tion is  poor.  This  gives  an  intermittent  ground,  which 
is  liable  to  burn  the  wire.  Crosses  occur  when  the  two 
sides  of  the  line  come  into  contact  with  each  other,  short- 
circuiting  part  of  the  lamps.  This  trouble  should  not 
occur  on  a  well  constructed  line. 

In  testing  for  grounds  and  open  circuits  an  ordinary 
magneto  is  about  the  best  thing  to  use.  A  portable  Wheat- 
stone  bridge  is  also  very  useful  and  a  high  reading  volt- 
meter can  often  be  used  to  good  advantage. 

Arc  lamp  circuits  should  be  tested  during  the  day  while 
the  power  is  off  for  grounds  and  open  circuits.  To  test 
for  grounds  connect  one  terminal  of  the  magneto  to  the 
line  and  the  other  to  a  water  pipe  or  some  other  good 
ground.  If  the  line  is  all  right  the  bell  should  not  ring. 
To  test  for  an  open  circuit  connect  the  magneto  across 
the  line.  If  the  circuit  is  closed  the  bell  will  ring. 

An  open  circuit  may  be  located  as  follows:  A  lamp 
circuit  supposed  to  be  open  at  O  is  shown  in  Fig.  22. 
A  and  B  represent  the  terminals  of  the  circuit  at  the 

43 


station  between   which  the  first  test  indicating  that  the 
line  was  open  was  made.     These  two  points  are  then  con- 

n  e  c  t  e  d   together 
and       grounded. 
jc    The  tester  goes  to 
,vj  /***  about    the    center 

U  j  /  I  (2) 

B'/  \  of      the      line      or 

— j^  I © @-°— @  @  @ I  some  other  con- 
venient point  where  he  disconnects  both  wires  from  a 
lamp  and  tests  the  two  halves  of  the  circuit  for  grounds, 
i.  e.,  connects  one  terminal  of  the  magneto  to  the  line 
and  grounds  the  other.  The  half  of  the  circuit  which  is 
closed  will  show  up  the  ground  at  A,  but  the  other  half 
will  give  no  indication.  By  proceeding  along  the  grounded 
part  of  the  circuit  and  repeating  this  test  at  intervals 
the  broken  place  can  be  located  between  narrow  limits, 
after  which  the  break  can  usually  be  found  by  inspection. 
Grounds  may  be  located  in  very  much  the  same  way  as 
shown  in  Fig.  23,  where  the  line  is  supposed  to  be 
grounded  at  G.  In  this  case  the  terminals  of  the  cir- 
cuit A  and  B  are  not  grounded  but  left  open.  The  tester 
goes  to  some  point  C  where  he  disconnects  a  lamp  and 
tests  both  sides  for  grounds.  The  side  011  which  the 
ground  exists  will  show  up.  By  proceeding  as  before  the 
position  of  the  ground  may  be  located. 

Locating  grounds  with  a  Whcatstone  bridge  obviates 
the  tester's  having  to  go  out  on  the  line.  Suppose  the 
circuit  shown  in 
Fig.  23  was  ground-  A 
ed  at  G.  With  the 
bridge  measure  the 
resistance  between, 
the  terminal  A  of 
the  line  and  the 
ground;  call  it  Ea.  Also  measure  between  B  and  the 
ground,  calling  it  Eb.  Then  the  distances  from  the  sta- 


tion  to  the  point  G  along  the  two  lines  are  proportional 
to   these   resistances. 

A  G     :     EG     ::     R  a     :     Eb 

A  simple  modification  of  the  "Wheatstone  bridge  method 
is  to  use  a  high  reading  voltmeter  while  the  lamps  are 
burning.  Readings  are  taken  between  each  side  of  the 
line  and  the  ground  and  these  are  proportional  to  the 
distances  along  each  side  of  the  line  to  the  ground. 


Care  of 
Electrical  Measuring  Instruments 

Electrical  measuring  instruments  should  be  handled 
carefully  and  not  subjected  to  any  jars  or  hammering. 

Portable  instruments  are  often  placed  in  positions 
where  they  are  subjected  to  a  strong  magnetic  field  or  to 
high  temperatures.  Both  of  these  cause  errors  in  the 
reading. 

In  the  permanent  magnet  type  of  direct  current  instru- 
ments if  the  temperature  is  increased  the  strength  of 
the  magnets  will  be  decreased  which  tends  to  decrease  the 
reading  of  the  instruments,  but  at  the  same  time  the 
strength  of  the  holding  spring  will  be  decreased  and  these 
two  errors  tend  to  neutralize  each  other.  As  a  general 
rule,  however,  these  meters  will  read  low  when  they  are 
hot.  In  the  ammeters  of  this  type  with  an  internal  shunt 
the  heat  from  the  shunt  will  usually  cause  the  instru- 
ment to  read  low.  Up  to  about  25  amperes  these  meters 
read  correctly,  but  above  that  they  should  not  be  left  in 
the  circuit  at  all  times.  Direct  current  meters  for  read- 
ing large  currents  should  be  provided  with  an  outside 
shunt. 

Errors  will  be  caused  by  stray  magnetic  fields,  the  size 
depending  upon  the  strength  of  the  field.  An  alternating 
current  field  if  weak  will  not  affect  a  direct  current  meter, 
but  if  strong  it  will  exert  a  de-magnetizing  effect  upon 
the  meter  and  cause  a  low  reading.  These  fields  may  be 
caused  by  any  electric  generator  or  motor,  a  conductor 
carrying  current,  or  by  other  meters.  Switchboard  meters 
should  be  shielded  from  the  effect  of  these  fields  by  an 
iron  case.  • 

Other  causes  of  errors  which  may  be  mentioned  are  the 
friction  of  pivots,  defective  springs  and  lack  of  balance 
of  moving  parts.  These  faults,  however,  should  not  be 
found  in  well  made  meters. 

46 


For  measuring  A.  C.,  current  transformers  and  not 
shunts  should  be  used.  Care  should  be  taken  that  no 
more  meters  are  connected  on  the  secondary  of  the  trans- 
former than  the  number  which  it  is  designed  to  carry. 
At  light  loads  the  ratio  of  transformation  is  not 
accurate  and  small  errors  will  be  introduced.  The 
secondary  of  both  current  and  potential  instrument  trans- 
formers on  high  potential  lines  should  be  grounded.  This 
not  only  protects  the  operator  but  prevents  errors  due  to 
static  electricity. 

In  the  A.  C.  induction  meters  the  error  due  to  small 
changes  in  frequency  should  be  slight. 

Eattling  and  humming  of  meters  is  caused  by  loose 
parts. 

In  the  D.  C.  wattmeters  the  case  may  become  per- 
manently magnetized  and  affect  the  reading. 

Wattmeters  should  be  inspected  at  least  once  a  year 
when  they  should  be  thoroughly  cleaned  and  the  pivot 
at  the  bottom  oiled.  The  creeping  of  wattmeters  is 
usually  due  to  vibration  of  the  wall  on  which  they  are 
fastened.  The  potential  coil  is  connected  to  the  line  at 
all  times  and  this  in  connection  with  the  starting  coil  gives 
a  small  torque.  Another  cause  is  the  connection  of  a 
meter  on  a  higher  voltage  than  that  for  which  it  is 
adjusted.  A  good  wattmeter  should  give  accurate  read- 
ings on  both  light  and  heavy  loads  under  a  wide  variation 
of  power  factor,  frequency  and  wave  form.  The  damping 
magnets  should  not  lose  their  magnetism  and  the  case 
should  be  moisture,  bug  and  dust  proof. 

Good  electrical  contact  is  extremely  important  with  all 
measuring  instruments.  This  is  particularly  important  in 
the  low  reading  milli-voltmeters  when  used  for  measur- 
ing current  with  external  shunt.  If  the  resistance  of  the 
meter  is  only  a  few  ohms,  a  corroded  or  dirty  terminal 
may  introduce  a  large  percentage  of  error. 


47 


Inside  Wiring 

The  Rules  of  the  National  Board  of  Fire  Underwriters 
published  in  the  National  Electric  Code  for  the  installa- 
tion of  light  and  power  apparatus  should  be  followed  in 
all  cases  where  no  municipal  ordinances  are  in  effect. 
The  following  are  some  of  the  requirements: 

In  all  electric  work  conductors,  however  well  insulated, 
should  always  be  treated  as  if  they  were  bare.  To  the 
end  that  under  no  condition,  existing  or  likely  to  exist, 
can  a  short  circuit  occur  and  that  all  leakage  from  con- 
ductor to  conductor,  or  between  conductor  and  the  ground, 
may  be  reduced  to  a  minimum. 

In  all  wiring  special  attention  must  be  paid  to  the 
mechanical  execution  of  the  work.  In  laying  out  an 
installation,  except  for  constant  current  systems,  every 
reasonable  effort  should  be  made  to  secure  distribution 
centers  located  in  easily  accessible  places,  at  which  points 
the  cut-outs  and  switches  controlling  several  branch  cir- 
cuits can  be  grouped  for  convenience  and  safety  of  opera- 
tion. The  load  should  be  divided  as  evenly  as  possible 
among  all  the  branches  and  all  complicated  and  unneces- 
sary wiring  avoided. 

Wires  must  not  be  smaller  than  No.  14  B.  &  S.  gauge, 
except  for  fixtures  and  flexible  cords  where  No.  18  may 
be  used. 

Tie  wires  must  have  an  insulation  equal  to  that  of  the 
conductors  which  they  confine. 

Wires  must  be  so  spliced  or  joined  as  to  be  both 
mechanically  and  electrically  secure  without  solder.  The 
joints  must  then  be  soldered  to  insure  preservation,  and 
covered  with  an  insulation  equal  to  that  on  the  con- 
ductors. 

Stranded  wires  must  be  soldered  before  being  fastened 
under  clamps  or  binding  screws,  and  whether  stranded  or 

48 


solid,  when  they  have  a  conductivity  greater  than  that  of 
No.  8  B.  &  S.  gauge,  they  must  be  soldered  into  lugs  for 
all  terminal  connections. 

The  wires  must  be  separated  from  contact  with  walls, 
floors,  timbers  or  partitions  through  which  they  pass,  by 
non-combustible,  non-absorptive,  insulating  tubes,  such  as 
glass  or  porcelain,  except  at  outlets  where  conduit  is 
used. 

Wire  should  run  over,  rather  than  under,  pipe  upon 
which  moisture  is  likely  to  gather. 

Where  underground  service  enters  a  building  through 
tubes,  the  tubes  shall  be  tightly  closed  at  the  outlet  by 
asphaltum  or  other  non-conductor  to  prevent  gases  from 
entering  the  building  through  such  channels. 

Overhead  wires  entering  the  basement  of  a  house  should 
do  so  through  a  conduit  passing  through  the  wall.  When 
entering  above  ground,  the  wires  should  pass  through 
insulating  tubes  slanting  upward. 

Automatic  cut-outs  must  be  placed  on  all  service  wires, 
either  overhead  or  underground,  as  near  as  possible  to 
the  point  where  they  enter  the  building  and  arranged  to 
cut  off  the  entire  circuit  from  the  house. 

Cut-outs  must  be  placed  at  every  point  where  a  change 
is  made  in  the  size  of  wire,  unless  the  cut-out  in  the 
larger  wire  will  protect  the  smaller. 

No  set  of  incandescent  lamps  requiring  more  than  660 
watts,  whether  grouped  on  one  fixture  or  several,  should 
be  dependent  upon  one  cut-out.  Special  permission  may 
be  obtained  of  the  Inspection  Department  for  departure 
from  this  rule  in  the  case  of  large  chandeliers. 

The  rated  capacity  of  fuses  must  not  exceed  the  allow- 
able carrying  capacity  of  the  wire  as  given  in  Table 
No.  3.  Circuit  breakers  must  not  be  set  more  than  30% 
above  the  allowable  carrying  capacity  of  the  wire  unless 
a  fusible  cut-out  is  also  installed  in  the 'Circuit. 

Switches  must  be  placed  on  all  service  wires,  either 
overhead  or  underground,  in  a  readily  accessible  place, 


as  near  as  possible  to  the  point  where  the  wires  enter  the 
building,  and  arranged  to  cut  off  the  entire  current. 

When  possible,  switches  should  be  so  wired  that  blades 
will  be  "dead"  when  the  switches  are  open.  They 
should  not  be  placed  so  that  they  tend  to  fall  closed. 

The  ground  wire  in  the  D.  C.  three-wire  system  must 
not  be  smaller  than  No.  6  B.  &  S.  gauge.  In  A.  C. 
systems  it  must  never  be  less  than  No.  6  B.  &  S.  gauge 
and  must  always  have  a  carrying  capacity  equal  to  that 
of  the  secondary  lead  of  the  transformer,  or  the  combined 
leads  where  transformers  are  connected  in  parallel.  On 
three-phase  systems  the  ground  wire  must  have  a  carry- 
ing capacity  equal  to  any  one  of  the  three  mains. 

FOR  OPEN  WORK.  For  open  work  approved  rubber  or 
"slow-burning  weatherproof "  insulated  wire  should  be 
used.  The  rubber  covered  wire  is  used  in  cellars  and  in 
other  places  subjected  to  moisture  or  acid  fumes. 

The  wires  must  be  rigidly  supported  on  non-combustible, 
non-absorptive  insulators  which  will  separate  the  wires 
from  each  other  and  from  the  surface  wired  over,  in 
accordance  with  the  following  table: 

Vnltnp-P  Distance   from  Distance  between 

surface.  wires. 

0  to  300  y2  inch  2y2  inches 

301  to  550  1  inch  4       inches 

Where  wiring  runs  along  flat  surfaces,  supports  at 
least  every  4y2  feet  are  required.  If  the  wires  are  liable 
to  be  disturbed,  the  distance  between  the  supports 
should  be  shortened. 

Wires  should  not  be  "  dead-ended "  at  rosettes,  but 
should  be  carried  beyond  them  for  a  few  inches  and 
securely  fastened  with  porcelain  cleats. 

FOR  MOULDING  WORK.  Moulding  work  should 
never  be  used  in  concealed  or  damp  places  or  where  the 
difference  of  potential  between  any  two  wires  in  the 
same  moulding  is  over  300  volts. 

As  a  rule  moulding  should  not  be  placed  directly  against 

50 


brick  walls  as  they  are  likely  to  sweat  and  thus  introduce 
moisture  into  the  moulding. 

Approved  rubber  insulated  wire  should  be  used. 

CONCEALED  KNOB  AND  TUBE  WORK.  This  is 
allowed  by  the  underwriters  rules  but  prohibited  by 
ordinances  in  a  great  many  cities. 

Approved  rubber  covered  wire  should  be  used.  The 
wire  must  be  separated  at  least  1  inch  from  the  surface 
wired  over  and  must  be  kept  at  least  10  inches  apart,  and, 
when  possible,  should  be  run  singly  on  separate  timbers 
or  studdings.  They  must  be  separated  from  contact  with 
walls,  floors,  timbers,  etc.,  through  which  they  pass  by 
insulating  tubes,  such  as  glass  or  porcelain. 

Eigid  supports  are  required  under  ordinary  conditions 
at  least  every  4^  feet,  but  a  generous  use  of  tubes, 
cleats,  or  knobs  is  advisable  in  places  where  the  circuits 
are  entirely  concealed  and  where  any  derangement  can 
not  be  observed. 

All  outlets  must  be  protected  by  insulating  tubing  or 
by  conduit.  In  cases  of  combination  fixtures  the  tubes 
must  extend  at  least  flush  with  the  outer  end  of  the 
gas  cap. 

CONDUIT  WIRING.  Conduit  wiring  is  the  best  and 
safest,  and  the  only  kind  allowed  in  fireproof  buildings. 
Iron  pipes  with  galvanized  or  enameled  interiors  are  most 
exclusively  used.  The  smallest  size  conduit  has  an 
interior  diameter  of  %  inch.  Care  should  be  taken  that 
the  insides  of  the  pipes  are  free  from  rough  spots  or 
projections.  The  entire  system  of  conduit  must  be  con- 
tinuous, and  permanently  and  effectively  grounded.  The 
inside  edge  of  bends  should  never  have  a  radius  of  less 
than  3%  inches,  nor  more  than  the  equivalent  of  four 
quarter  bends  should  be  placed  between  two  outlets. 

Eubber  covered  wire  should  be  used. 

In  A.  0.  circuits  it  is  necessary  and  in  D.  C.  it  is 
advisable  that  the  two  sides  of  the  circuit  should  be 
contained  in  the  same  conduit. 


Calculation  of  Size  of  Wire 

The  size  of  an  electrical  conductor  is  usually  given  in 
circular  mils.  A  mil  is  one  thousandth  of  an  inch,  and  a 
circular  mil  is  the  area  of  a  circle,  the  diameter  of  which 
is  one  mil. 

To  obtain  the  area  of  a  conductor  in  circular  mils, 
knowing  the  diameter,  all  that  is  necessary  is  to  multiply 
the  diameter  expressed  in  mils  by  itself,  i.  e.,  square  the 
diameter.  For  example  a  ^-inch  cable  has  a  diameter 
of  250  mils  and  an  area  250  X  250  —  62,500  circular  mils. 

Every  conductor  offers  some  resistance  to  the  flow  of 
current.  This  resistance  increases  as  the  length  increases 
and  decreases  as  the  cross  section  increases.  For  metal 
conductors  this  resistance  increases  as  the  temperature 
rises.  The  resistance  of  one  foot  of  copper  wire  with  a 
cross  section  area  of  one  circular  mil  has  been  found 
to  be  10.8  ohms  at  75°  F.  For  wiring  calculations  this 
is  commonly  taken;  as  11.  ohms.  The  resistance  of  any 
conductor  is,  therefore 

„  _  11  X  L 

~K~ 

L  =  Length  of  the  conductor  in  feet.  A  =  cross  section 
area  in  circular  mils. 

For  example  1,000  feet  of  %-inch  cable  with  an  area  of 
62,500  circular  mils  has  a  resistance  of 
11  X  1000 


The  voltage  (E)  consumed  when  current  flows  through 
a  conductor  is  equal  to  the  product  of  the  current  in 
amperes  (I)  and  the  resistance  in  ohms  (R). 

E  =  IXR 

If    the    cable    referred    to    above    were    carrying    100 
amperes,  the  volts  drop  in  the  cable  would  be 
E  =  100X0.176  =  17.6  volts. 

52 


From  the  two  equations  already  given  a  third  can  be 
obtained  by  substituting  the  value  of  (R)  from  the  first 
into  the  second 

_IX11  XL 
E~      —A" 

11  XL  XI 

A  =  — 


E 

This  equation  is  used  for  finding  the  size  of  wire  (A) 
in  circular  mils  necessary  to  carry  a  known  current  over 
a  given  distance  with  a  certain  allowable  drop  in  voltage. 
For  example:  What  size  of  wire  will  be  necessary  to 
carry  100  amperes  over  a  distance  of  300  feet  with  volt- 
age drop  of  5?  To  carry  the  circuit  over  a  distance  of 
300  feet  will  require  600  feet  of  wire. 

A  =  11X6;OX10°  =132,000   circular  mils. 

t). 

Looking  up  in  the  table  the  nearest  size  is  No.  00.  The 
current  values  given  in  the  table  must  not  be  exceeded 
and  in  cases  where  the  allowable  drop  is  large  the  values 
given  in  the  table  and  not  the  drop  will  determine  the 
size  of  the  wire  to  be  used. 

To  calculate  the  drop  it  is  necessary  to  know  the  cur- 
rent flowing  in  the  circuit.  In  incandescent  lamp  circuits 
this  depends  on  the  efficiency  of  the  lamps  and  on  the 
voltage  and  may  be  calculated  approximately  from  the 
following  formula: 

__  N-Z-P 
~E~ 

I  =  Current  in  amperes.  N  =  Number  lamps  connected 
in  parallel  in  the  circuit.  P  =  Candle  power  of  lamps. 
Z  =  Watts  consumed  per  c.  p.  in  the  lamps.  E  =  Voltage 
of  the  circuit. 

The  following  values  of  Z  will  give  fairly  good  results. 

3.5  for  110  volt  carbon  filament  incandescent  lamps. 

4.0  for  220  volt  carbon  filament  incandescent  lamps. 


Tungsten  and  Tantalum  lamps  are  rated  in  watts,  in 
which  case  this  value  is  substituted  for  P  Z,  the  formula 
becoming 

N  X  W 
~!T 

W  =  watts  consumed  in  one  lamp. 

In  most  cases  the  distance  to  be  used  in  calculating 
the  size  of  wire  should  be  an  average,  for  example  with 
a  circuit  200  feet  long  with  lamps  distributed  over  the 
last  100  feet,  the  distance  taken  should  be  100  +  y2 
(100)  -150  feet  of  circuit. 

The  allowable  drop  is  usually  given  in  per  cent,  of  the 
voltage.  To  obtain  the  actual  volts  drop,  multiply  the 
voltage  by  the  per  cent,  drop,  pointing  off  two  places, 
i.  e.,  a  2%  drop  on  a  100  volt  line  would  be  100  X  .02  = 
2  volts. 

What  size  of  wire  is  necessary  for  a  110  volt  incan- 
descent lighting  circuit  400  feet  long  carrying  40 — 16  c.  p. 
carbon  filament  lamps.  The  lamps  are  distributed  over 
the  last  50  feet  and  a  2%  voltage  drop  is  allowed. 

The  distance  to  the  center  of  distribution  is: 
350  +  %  X  50  =  375  feet.     Therefore  375  X  2  =  750  feet  of 
wire  should  be  used  in  the  calculations. 

40  X  16  X  3.5 
The  current  I  = j^TT ~  20<4  amP- 

The  allowable  drop— D  =  110  X  .02  =  2.2  volts. 

11  X  750  X  20.4 
A=—  —=76500   circular  mils. 

4.4 

The  nearest  size  to  this  is  No.  1  B.  &  S.  gauge.  The 
carrying  capacity  is  sufficient  for  the  current. 


54 


TABLE   3 

Carrying  Capacity  of  Copper  Wires 

The  following  table,  showing  the  allowable  carrying 
capacity  of  copper  wires  and  cables  of  98°/0  conductivity, 
according  to  the  standard  adopted  by  the  American 
Institute  of  Electrical  Engineers,  must  be  followed  in 
placing  interior  conductors. 

For  insulated  aluminum  wire  the  safe  carrying  capacity 
is  84%  of  that  given  in  the  following  tables  for  copper 
wire  with  the  same  kind  of  insulation. 


B.  &  S.  Gauge 

Circular  Mils. 

Table  A. 
Rubber  Insulation. 
Amperes. 

Table  B. 
Other  Insulations. 
Amperes. 

18 

1,624 

3 

5 

16 

2,583 

6 

8 

14 

4,107 

12 

16 

12 

6,530 

17 

23 

10 

10,380 

24 

32 

8 

16,510 

33 

46 

6 

26,250 

46 

65 

5 

33,100 

54 

77 

4 

41,740 

65 

92 

3 

52,630 

76 

110 

2 

66,370 

90 

131 

1 

83,690 

107 

156 

0 

105,500 

127 

185 

00 

133,100 

150 

220 

000 

167,800 

177 

262 

0000 

211,600 

210 

312 

Circular  Mils. 

200,000 

200 

300 

300,000 

270 

400 

400,000 

330 

500 

500,000 

390 

590 

600,000 

450 

680 

700,000 

500 

760 

800,000 

550 

840 

900,000 

600 

920 

1,000,000 

650 

1,000 

1,100,000 

690 

1,080 

1,200,000 

730 

1,150 

1,300,000 

770 

1,220 

1,400,000 

810 

1,290 

1,500,000 

850 

1,360 

1,600,000 

890 

1,430 

1,700,000 

930 

1,490 

1,800,000 

970 

1,550 

1,900,000 

1,010 

1,610 

2,000,000 

1,050 

1.670 

The  lower  limit  is  specified  for  rubber-covered  wires  to  prevent 
gradual  deterioration  of  the  high  insulations  by  the  heat  of  the 
wires,  but  not  from  fear  of  igniting  the  insulation.  The  question 
of  drop  is  not  taken  into  consideration  in  the  above  tables. 

65 


TABLE  4 

Properties  of  Copper  Wire 

English  system — Brown  &  Sharpe  gauge. 


Numbers  . 

Diameters 
in  mils. 

Areas  in 
circular  mils. 
C.  M.=d2. 

Weights 
10GJ  ft. 
Pounds. 

Resistance 
per  1000  ft.  in 
International 
ohms. 
At  75°  F. 

0000 

460. 

211  600. 

641. 

.049  66 

000 

410. 

168  100. 

509. 

.062  51 

00 

365. 

133  225. 

403. 

.078  87 

0 

325. 

105  625. 

320. 

.099  48 

1 

289. 

83  521. 

253. 

.125  8 

2 

258. 

66  564. 

202. 

.157  9 

3 

229. 

52441. 

159. 

.200  4 

4 

204. 

41  616. 

126. 

.252  5 

5 

182. 

33  124. 

100. 

.317  2 

6 

162. 

26  244. 

79. 

.400  4 

7 

144. 

20  736. 

63. 

.506  7 

8 

128. 

16  384 

50. 

.641  3 

9 

114. 

12  996. 

39. 

.808  5 

10 

102. 

10  404. 

32. 

1.01 

11 

91. 

8  281. 

25. 

1.269 

12 

81. 

6  561 

20. 

1.601 

13 

72. 

5  184. 

15.7 

2.027 

14 

64. 

4  096. 

12.4 

2.565 

15 

57. 

3  249. 

9.8 

3.234 

16 

51. 

2  601. 

7.9 

4.04 

17 

45. 

2  025. 

6.1 

5.189 

18 

40. 

1  600. 

4.8 

6.567 

19 

36. 

1  296. 

3.9 

8.108 

20 

32. 

1  024. 

3.1 

10.26 

21 

28.5 

812.3 

2.5 

12.94 

22 

25.3 

640.1 

1.9 

16.41 

23 

22.6 

510.8 

1.5 

20.57 

24 

20.1 

404. 

1.2 

26.01 

25 

17.9 

320.4 

.97 

32.79 

26 

15.9 

252.8 

.77 

41.56 

27 

14.2 

201.6 

.61 

52.11 

28 

12.6 

158.8 

.48 

66.18 

29 

11.3 

127.7 

.39 

82.29 

30 

10. 

100. 

.3 

105.1 

31 

8.9 

79.2 

.24 

132.7 

32 

8. 

64. 

.19 

164.2 

33 

7.1 

50.4 

.15 

208.4 

34 

6.3 

39.7 

.12 

264.7 

35 

5.6 

31.4 

.095 

335.1 

36 

5. 

23. 

.076 

420.3 

56 


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Force,  Work  and  Power 

A  force  may  be  defined  as  an  action  which  changes 
or  tends  to  change  the  relative  position  of  a  body.  It  is 
usually  expressed  in  pounds. 

Work  is  the  exertion  of  a  force  through  space.  Work 
must  always  be  accompanied  by  motion,  and  is  measured 
by  the  product  of  the  force  and  the  distance  through 
which  it  acts. 

Work  =  Force  X  Distance. 

The  unit  of  work  usually  employed  is  the  foot-pound,  i.  e., 
the  work  done  when  a  force  of  one  pound  is  exerted 
through  a  distance  of  one  foot. 

Power  is  the  rate  of  doing  work.  The  unit,  the  horse- 
power,* is  the  amount  of  power  required  to  lift  550  Ibs. 
at  a  uniform  velocity  of  one  foot  per  second. 

1  H.  P.  =  550  ft.  Ibs.  per  sec.  =  33,000  ft.  Ibs.  per  min. 
=  1,980,000  ft.  Ibs.  per  hr. 


*United   States   standard. 


58 


Electrical  Energy 

The  power  that  is  transmitted  by  any  electric  circuit 
depends  on  the  current  and  the  voltage.  The  unit,  the 
watt,  is  the  amount  of  power  obtained  from  one  ampere 
at  one  volt.  This  unit  is  too  small  for  ordinary  purposes 
and  the  kilowatt  equal  to  1000  watts  is  used. 
For  D.  C.  circuits 

W  =  C  X  E. 
W  =  Power  in  watts. 
C  —  Current   in   amperes. 
E  =  Electromotive  force  in  volts. 

In  A.  C.  circuits  the  entire  current  is  not  always  avail- 
able for  doing  work.  This  calls  for  another  term  in  the 
energy  equation,  the  power  factor,  which  is  the  ratio 
of  the  current  available  for  power  to  the  total  current. 
For  single-phase  A.  C.  circuits  the  equation  becomes 

W  =  G  X  E  X  P. 
P  =  Power  factor  of  the  circuit. 

For  two-phase  A.  C. 

W  =  2XCXEXP. 

For  three-phase   A.   C. 

W  =  1.73XCXEXP. 


Electrical  and  Mechanical 
Conversion   Factors 

1  H.P.=     746  watts  =  .746  kw. 

1  kw.    =  1.344  H.P.  =  approx.  1J^  H.P. 


59 


Measurement  of  Heat 

The  British  Thermal  Unit  (B.  T.  U.)  is  the  unit  usually 
employed  in  heat  measurements.  It  is  that  quantity 
of  heat  required  to  raise  one  pound  of  pure  water  1°  F. 
at  or  near  39.1°  F.  This  unit  varies  slightly  as  the  density 
of  the  water  changes,  but  for  ordinary  calnihit  ions  it  is 
assumed  to  be  constant. 

The  Metric  unit  is  the  Calorie  or  quantity  of  heat 
required  to  raise  one  kilogram  of  water  1°  ( '.  at.  its 
maximum  density  near  4°  C. 

1  B.T.U.  =  .252  calories. 
1  Calorie  =  3.968  B.T.U. 

The  Small  Calorie  is  the  quantity  of  heat  required  to 
raise  one  gram  of  water  1°  C.  at  or  near  4°  C. 

1  Calorie  =  1000  Small  Calories. 


Mechanical  Equivalent  of  Heat 

The  Mechanical  Equivalent  of  Heat  is  the  number  of 
units  of  mechanical  energy  equivalent  to  a  unit  of  heat 
energy.  This  value  has  been  found  to  be 

1  B.T.U.  =  778  ft.  Ibs. 
1  H.P.  hr.  =  2,545  B.T.U. 
1  K.W.  hr.  =  3,412  B.T.U. 

The  Thermal  Capacity  of  a  body  is  the  amount  of  heat 
required  to  raise  it  one  degree.  The  ratio  between  this 
amount  and  that  required  to  raise  an  equal  weight  of 
water  at  its  maximum  density  one  degree  is  the  Specific 
Heat  of  the  substance. 


60 


Calculation  of  Temperature  by  the 
Rise  in  Resistance 

The  resistance  of  metal  conductors  increases  as  the 
temperature  rises.  The  change  in  resistance  per  ohm 
per  degree  rise  in  temperature  is  called  the  temperature 
co-efficient.  If  E0  is  the  resistance  of  a  conductor  at  0°  C 
and  a,  the  temperature  co-efficient  for  that  conductor, 
then  its  resistance  at  t°C  is 

Rt=R0  (1  +  at  ) 

When   the   resistance   of  a   conductor   at  ti°C  is   known 
and  the  resistance  at  I^C  is  desired,  the  equation  becomes 

R2=Ri  (i  +  Itl) 

The  A.  I.  E.  E.  temperature  co-efficient  for  commercial 
copper  wire  is  0.0042  per  °C.  Using  this  value  the  equa- 
tion for  copper  conductors  becomes 

(1-f  .0042  t2) 
?*— *i  (i  +  .0042  tj 

The  most  common  application  of  the  resistance  formula 
is  to  calculate  the  temperature  of  a  conductor  knowing 
its  resistance  also  the  resistance  and  temperature  of  the 
conductor  when  cold.  Solving  for  t2  the  equation  becomes 


For  copper  conductors  with  a  =  0.0042 
t2=  |*  (238  +  0-238 

The    temperature    co-efficient    for    aluminum    is    0.0039 
for  1°  C.    For  steel  it  is  0.005  and  brass  0.0038. 


Horse  Power  Calculations 


BOILER  PRESSURE 


rid.  24. 


ATMOSPHERIC   PRESSURE 


To  measure  the  available  horse  power  supplied  to  an 
engine,  it  is  necessary  to  know  the  steam  pressure  on  the 
face  of  the  piston  at  all  times  during  the  forward  stroke. 
Also  the  steam  pressure  opposing  the  piston  on  the  return 
stroke.      These    pressures    are 
measured     by    an    instrument 
called    an    indicator    which    is 
connected    on    a    pipe    leading 
from     the     cylinder     of     the 
engine.    This  instrument  makes 
a       diagram       a  s 
shown   in   Fig.   24, 
representing     the 
pressure      in      the 
cylinder    during 
ZERO  PRESSURE™  'the      complete 

forward  and  backward  stroke.  The  average  height  of 
this  figure  represents  the  effective  pressure  available  for 
doing  work  during  one  revolution  of  the  engine.  This  is 
called  the  Mean  Effective  Pressure  or  M.E.P. 

The  value  of  the  horse  power  obtained  by  using  the 
mean  effective  pressure  is  called  the  Indicated  Horse 
Power  or  I.H.P. 

TTTP  -PXLXAXN 
33,000 

P  =  Mean  effective  pressure  in  pounds. 
L  =  Length  of  the  stroke  of  the  engine  in  feet. 
A  =  Area  of  the  piston  head  in  square  inches. 
N  =  Speed  of  engine  in  revolutions  per  minute. 
33,000  =  The   number    of   foot-pounds  per   minute   in    a 
horse  power. 

This  formula  gives  the  horse  power  on  one  end  of  the 
cylinder  only,  i.  e.,  for  a  single  acting  engine. 

62 


The  value  of  the  mean  effective  pressure  depends  on 
the  maximum  steam  pressure,  the  percentage  of  stroke 
which  has  taken  place  when  cut  off  occurs  and  on  the 
back  pressure,  i.  e.,  whether  the  engine  is  exhausting  into 
the  air  or  if  a  condenser  is  used  and  if  so  on  the  amount 
of  vacuum. 

The  horse  power  available  at  the  pulley  is  called  the 
Developed  Horse  Power  or  D.H.P.  and  may  be  obtained 
from  the  following  formula: 

D.H.P.  =~n  G  X  A  X  N 


33,000 
?r=  3.1416 

G  =  Difference  in  pull  on  two  sides  of  the  belt. 
A  =  Eadius  of  the  pulley  in  feet. 
N  —  Speed  of  pulley  in  revolutions  per  minute. 

The  mechanical  efficiency  of  the  engine  is 
D.H.P. 


E  = 


I.H.P. 


Atmospheric  Pressure 

The  pressure  due  to  the  atmosphere  is  14.7  Ibs.  per 
square  inch  at  the  sea  level.  This  decreases  as  the  eleva- 
tion increases  until  at  one  mile  it  is  about  12  Ibs.  For 
a  rough  approximation  it  may  bei  assumed  that  the 
pressure  decreases  one-half  pound  per  1,000  feet  of 
elevation. 

The  pressure  14.7  Ibs.  per  square  inch  corresponds  to 
the  pressure  of  a  column  of  mercury  29.92  inches  in 
height,  or  a  column  of  water  33.9  feet. 


63 


Weight  of  Substances 

(Kent's  Mechanical  Engineer's  Pocket  Book.) 

Weight  of  Water 

The  weight  of  a  cubic  foot  of  water  varies  with  the 
temperature.  The  point  of  maximum  density  is  39.1°  F. 

At    32     °  F freezing  point   62.418  Ibs. 

39.1°  F maximum  density    62.425  Ibs. 

62     o  F    62.355  Ibs. 

212     °  F.    boiling  point  under  one  atmos. .  .59.76     Ibs. 

The  boiling  point  of  water  depends  on  the  pressure  to 
which  it  is  subjected  rising  as  the  pressure  increases. 
Under  a  pressure  of  one  atmosphere  (14.7  Ibs.  per  square 
inch)  it  boils  at  212°  F. 

The  specific  gravity  of  a  substance  is  the  ratio  of  its 
weight  to  that  of  an  equal  volume  of  water  at  its  maxi- 
mum density. 


64 


TABLE  6 
Weight  and  Specific  Gravity  of  Metals 

(Kent's  Mechanical  Engineer's  Pocket  Book.) 


Specific  Gravity 
Approximate  Mean  Value 
used  hi  Calculation 
of  Weight. 

Weight  per 
Cubic  Foot, 
Pounds. 

Aluminum 

2  67 

167 

Antimony.  .      .             

6  76 

422 

Bismuth 

9  82 

612 

Brass:      Copper  +  Zinc. 
80           20 

8  60 

536 

70           30  
60           40 

8.40 
8  38 

524 
521 

50           50        

8  20 

511 

Bronze:  Copper,  95  to  80  ( 

8  85 

552 

Tin,         5  to  20  j 
Gold  pure 

19  26 

1201 

Copper    . 

8  85 

552 

Indium 

22  38 

1396 

Iron  cast  .   . 

7  22 

450 

1  '    wrought 

7  70 

480 

Lead          .         ...                  .       . 

11  38 

710 

Manganese 

8 

499 

Magnesium. 

1  75 

109 

(     323 
Mercury     .                             •<     60° 

13.62 
13  58 

849 
847 

/    212° 
Nickel.  .  . 

13.38 
8  8 

834 
549 

Platinum  

21  5 

1347 

Silver     . 

10  51 

655 

Steel... 

7  85 

490 

Tin.     .  . 

7  35 

458 

Zinc  

7  00 

437 

65 


TABLE  7 

Weight    and   Specific    Gravity   of 
Stones,  Brick,  Cement,  Etc. 

(Kent's  Mechanical  Engineer's  Pocket  Book.) 


Pounds  per 
Cubic  Foot. 

Specific 
Gravity. 

Asphaltum  

87 

1  39 

Brick,  Common. 

112 

1  79 

"    Pressed  

135 

2  16 

"    Fire  

140  to  150 

2  24  to  2  4 

Brickwork  in  mortar.  .    .  . 

100 

1  6 

"  cement 

112 

1  79 

Cement,  Portland,  loose    . 

92 

in  barrels  

115 

Clay  

120  to  150 

1  92  to  2  4 

Concrete 

120  to  155 

1  92  to  2  48 

Earth,  loose  

72  to    80 

1  15  to  1  28 

rammed  

90  to  110 

1  44  to  1  76 

Gneiss    i 

160  to  170 

2  56  to  2  72 

Granite  f  
Gravel  ... 

100  to  120 

16    to  1  92 

Lime,  quick,  in  bulk  

50  to    60 

.8   to    .96 

Limestone 

140  to  185 

2  30  to  2  90 

Marble  

160  to  180 

2  56  to  2  88 

Masonry  dry  rubble 

140  to  160 

2  24  to  2  56 

dressed  ... 

140  to  180 

2  24  to  2  88 

Mortar  . 

90  to  100 

1  44  to  1  6 

Pitch  

72 

1  15 

Sand  .  .  . 

90  to  110 

1  44  to  1  76 

Sandstone. 

140  to  150 

2  24  to  2  4 

Slate  

170  to  180 

2.72  to  2.88 

Tile.     .  . 

110  to  120 

1  76  to  1  92 

66 


TABLE  8 

Metric  System 

Measures  of  Length 

10  millimeters   (mm)    ...  =1  centimeter    cm. 

10  centimeters    =1  decimeter    * dm. 

10  decimeters   =1  meter    m. 

10  decameters    =1  hectometer    Hm. 

10  hectometers =1  kilometer    Km. 

Measures  of  Surface  (Not  Land) 

100  square  millimeters  . .  =1  square  centimeter  .  .  sq.  cm. 
100  square  centimeters  .  =1  square  decimeter  ...sq.  dm. 
100  square  decimeters  .  .  =1  square  meter  sq.  m. 

Measures  of  Volume 

1000  cubic  millimeters  . .  =1  cubic  centimeter  .  .  .cu.  cm. 
1000  cubic  centimeters  .  =1  cubic  decimeter  . . .  .cu.  dm. 
1000  cubic  decimeters  . .  =1  cubic  meter  cu.  m. 

Measures  of  Capacity 

10  milliliters  (ml.)    =1  centiliter   cl. 

10  centiliters   =1  deciliter    dl. 

10  deciliters    =1  liter    1. 

10  liters   =1  decaliter    Dl. 

10  decaliters   =1  hectoliter HI. 

10  hectoliters    =1  kiloliter    Kl. 

Measures  of  Weight 

10  milligrams  (mg) =1  centigram    eg. 

10  centigrams    =1  decigram    dg. 

10  decigrams    =1  gram    g. 

10  grams =1  decagram     Dg. 

10  decagrams    =1  hectogram Hg. 

10  hectograms    =1  kilogram .Kg. 

1000  kilograms =1  ton    T. 

The  gram  is  the  weight  of  1   cu.  cm.  of  pure  distilled 
water  at  39.2°  F. 


TABLE  9 

Conversion  Factors 

1  mm =        0.03937  in. 

1  cm =        0.3937     in. 

1m =      39.37         in.    =  3.281  ft.  =  1.094  yds. 

1  Km =  1093.6           yds.  =    .621  miles. 

1  in =    25.4  mm =  2.54     cm. 

1  ft =    30.5    cm -    0.305  m. 

1  yd =      0.914  m. 

1  mi =  1609  m =  1.609  km. 

1  sq.   mm =  0.00155  sq.  in. 

1   sq.  cm —  0.155     sq.  in. 

1  sq.  m =  1550  sq.  in.  =  10.764  sq.  ft.  =  1.196  sq.  yd. 

1  hectom =  11959.9  sq.  yds.  =  2.471  acres. 

1  sq.  in =    645.2       sq.  mm.. . .  =  6.452  sq.  cm. 

1  sq.  f t =s    929.         sq.  cm =  0.093  sq.  m. 

1  sq.  yd =        0.836  sq.  in. 

1  acre    =  4046.87     sq.  m =  0.4047  hectare. 

1  cu.  cm =    0.061  eu.  in.  =  0.00211  pts.  (U.S.  liquid) 

1  liter    =  61.02   cu.   in.  =  1.057      qts.    (U.S.   liquid) 

1  liter =    0.2642  gal.  (U.S.  liquid) 

1  gal.  (U.S.Liq.)=    3.785  liters. 
1  bu.    (U.S.)  . . .  .=  35.239  liters 

1  gram    =       15.43  grains. .  =  0.0022  Ibs.  avoird. 

1  kilogram  (kg.)=        2.205  Ibs.  avoirdupois. 
1  metric    ton    .  ;=  2204.62  Ibs.  avoirdupois. 


TABLE  10 

Thermometer   Scales 

There  are  two  thermometer  scales  in  general  use  in  this 
country  at  the  present  time,  the  Fahrenheit  and  the  Centi- 
grade. On  the  Fahrenheit  scale  the  melting  point  of  ice 
is  32°  and  the  boiling  point  of  water  at  sea-level  is  212°. 
On  the  Centigrade  scale  0°  is  the  melting  point  of  ice 
and  100°  the  boiling  point  of  water.  Another  scale,  the 
Absolute,  is  sometimes  used.  This  takes  its  zero  at  a 
point  assumed  to  be  the  lowest  temperature  that  can 
exist.  This  point  was  calculated  from  the  contraction  of 
gases  when  cooled  and  found  to  be — 273°  C,  i.  e.,  273° 
below  zero  Centigrade.  The  size  of  the  degrees  of  the 
Centigrade  and  Absolute  scales  is  the  same,  so  to  con- 
vert degrees  Centigrade  to  Absolute  all  that  is  necessary 
is  to  add  273. 

To  convert  degrees  Centigrade  to  Fahrenheit  multiply 
by  1.8  and  add  32. 

To  convert  degrees  Fahrenheit  to  Centigrade,  subtract 
32  and  divide  the  result  by  1.8.  Care  should^  be  taken 
that  the  sign  of  the  result  is  correct  when  the  temperature 
is  below  the  freezing  point  of  water. 

(The  constant  1.8  is  obtained  as  follows:  Between  the 
freezing  and  boiling  points  of  water  there  are  100°  C  and 
212°— 32°  =  180°  F.  Therefore,  1°  C  =  1.8°  F.  The  factor 
32  arises  from  the  fact  that  0°  C  corresponds  to  32°  F.) 


69 


/TJ 


Mensuration 


Area   of  triangle=base  X  %    altitude=A  X 


Area   parallelogranu=base  X  altitude=A  X  B 

Area  of  trapezoid=:%  (sum  of  parallel  sides) 
X  altitude^  %    (A+C)  X  B 

Area  of  a  trapezium— Divide  into  triangles  and  find 
area  of  each  separately. 


Diagonal  of  a  8quare=the    square    root    of    twice 
the  square  of  one  side=:1.414  A 

Diagonal  of  a  rectangle^the  square  root  of  the  sum 
of  the  squares  of  the 
adjacent  sides. 


Circumference  of  a  circle^Diameter      X  3.1416 
rr2  X  radius    X  3.1416 

Area  of  a  circle=The  square  of  the  radius  X  3.1416 
=the     square     of     the     diameter 
X  .7854 

A  regular  polygon,  one  whose  sides  and  angles 
are  all  equal,  areac=%  sum  of  the  sides  X  per- 
pendicular from  the  center  to  one  of  the  sides. 


The  surface  of  a  sphere=4  X  radius 

squared  X  3.1416 
Contents  of  a   sphere=4/3  X  radius  cubed  X  3.1416 


70 


Surface  of  a  cylinder=:area  of  both  ends  +  length  X 

circumf  erenc  e. 
Contents  of  a  cylinder=:area  of  one  end  X  length. 


Surface    of    a   cone^area    of  ..base  +  circumference 
of  base  X  %    the  slant  height. 

Contents  of  a  cone=area  of  base  X  %  altitude. 


To  square  a  number  multiply  it  by  itself.  To 
cube  a  number  multiply  it  by  itself  and  multiply 
the  result  by  the  number. 


INDEX 


Page 

Adjustment  of  Arc  Lamps      ........      20 

Arc  Voltage — Enclosed    Lamps       .         .         .         .  6,   7,   8 

Arc  Voltage — Flame    Lamps 29 

Striking    Point 30 

Aluminum. 

Carrying  Capacity .55 

Temperature    Coefficient 61 

Weight 65 

Ammeters,   Care   of 46 

Arc    Lamp. 

Adjustment 20 

Carbons 13 

Connecting    to    line 14,   30 

Dash  Pots 19 

Gas  Caps 16 

Globes 12,    15 

Suspension        .         .         .         .         .  .         .         .         .41 

Wiring  42 

See  Enclosed  Arc  Lamps. 
See  Flame   Arc   Lamps. 
See  Miniature  Arc  Lamps. 
See  Troubles. 

Arc  Voltage. 

Enclosed   Lamps 6,   7,   8 

Flame   Lamps 29 

Areas,  Geometrical  Figures 70 

Atmospheric  Pressure 63 


Brass. 

Temperature    Coefficient 61 

British  Thermal   Unit 60 

Building  Material,   Weight  of 66 


Calorie 60 

Carbons. 

Bridge   Core 26 

Care  of 13,  30 

Enclosed   Arc   Lamp 13 

Flame  Arc  Lamp 29 

Graphitization 18 

Life 16,  30 

Care  of  Arc  Lamps. 

Enclosed 13,  15 

Flame .         .         .       29,  32 

Centigrade   Thermometer   Scale       .         .         .         .         .         .        .69 

Centigrade  to  Fahrenheit 69 

Choke  Coils 8 

Clock  Feed  Flame  Lamps .23 

72 


INDEX— Continued. 

Clutches.  Pa&e 

Arc  Lamp 6,   33 

Slipping 20 

Colors,    Reflecting    Power    of 34 

Columbia  Enclosed  Arc  Carbons 13 

Constant   Current   Apparatus 35 

Conversion  Factors. 

Electrical-Mechanical        ........      59 

Mechanical-Heat 60 

Metric-English 68 

Copper. 

Carrying  Capacity  .         .         .         .         .         .         .         .55 

Properties  of  Copper  Wire 56 

Temperature    Coefficient 61 

Weight   of 65 


Dash  Pots,  Arc  Lamp 19,   33 

Dynamos,    Arc    Lamp       .         .         .         .         .         .         .         .         .35 


Economizer 23 

Burned    out 31 

Enclosed  Arc  Lamps. 

A.  0.  Multiple 7 

Carbons     ...........  13 

D.    C.    Multiple 5 

Gas  Caps .16 

Series 9 

Series-Multiple 10 

Twin    Carbon 7 

Energy,     Electrical 59 


Fahrenheit  Thermometer  Scale        .         .         .         .         .         .         .69 

Fahrenheit  to   Centigrade        ........  69 

Flame    Arc    Lamps  .         .         .         .         .         .         .         .         .22 

Clock  Feed 23 

Distribution 28 

Economizer        ..........  23 

Efficiency 22 

Gravity  Feed 25 

Magazine 26 

Motor  Feed 24 

Regenerative      ..........  27 

Force,  Work  and  Power         ........  58 

G 

Gas  Caps t  16 

Globes. 

Arc    Lamp 12 

Cleaning 15 

Graphitization  of  Carbons        ........  18 

Gravity  Feed  Flame  Lamp      .         .         .         .         .         .         .         .25 

Grounds  on  Arc  Lamp  Circuits 43 

78 


I  N  D  B  X—  Continued. 

H 

Heat.  Page 

Units          ...........      60 

Mechanical  Equivalent  of  .......  60 

Horse   Power   Calculations      .         .         .         .         .         .         .         .62 

I 

Intensified  Arc  Lamps     ..........      11 

Intensity   of   Interior   Illumination          ......      34 


Jumping  of  Arc  Lamp  Carbons      .         .  .         .         .         .19 

L 

Light  Reflected  by  Various  Colors  —  Table    .....  34 

Line    Work       ...........  41 

Locating  Faults        .........  43 

M 

Magazine    Flame    Lamp  ......         .         .26 

Measuring    Instruments,     Electrical        .         .         .         .  .46 

Mechanical  Equivalent  of  Heat        .......      60 

Mensuration      ...........      70 

Mercury  Arc  Rectifier      .........      35 

Metals,    Weight    of          .........      65 

Metric  System  ..........      67 

Conversion    Factors          ........      68 

Miniature  Arc  Lamps      .         .         .         .         .         .         .         .         .11 

Motor  Feed  Flame  Lamp        .         .         .         .         .         .         .         .25 

Motors,    Current   Required      .         .         .         .         .         .         .         .57 

Multiple    Arc    Lamps      .         .         .         .         .         .         .         .         .  5,    7 

N 

National   Electric   Code    .........      48 

O 

Open  Circuit  on  Arc  Lamp  Circuits        ......      43 

P 

Power  Factor   .........         .         .59 

Power,    Force   and  Work        ........      58 

Power   H.P.    Calculations        ........      62 

B 

Regulator,  Constant  Current    ........  38 

Resistance. 

Calculation    of           .........  53 

Compensating  for  Arc   Lamps        ......  10 

Regulating  for  Arc  Lamps      .......  6 

Starting   for   Arc    Lamps        .......  9 

S 

Series  Arc  Lamps    .......         -.         .         .        9 

Series-Multiple  Arc  Lamps      .         .         .         .         .         .         .         .10 

Short-Life  of  Carbons      ......         .         .       •  .      17 

Silver  Tip  Flame  Carbons      ........      29 

74 


I N  D  E  X— Continued. 

Page 
Size  of  Wire 52,   56 

Station    Equipment  .         .         .         .         .         .         .         .         .35 

Steel. 

Temperature  Coefficient    .         .         .         .         .         .         .         .61 

Weight 65 

Striking  Point  of  Flame  Arc  Lamps 30 

Switch  Boards 40 

T 

Temperature. 

Calculating   by   Rise    in    Resistance 61 

Thermometer    Scales        .........      69 

Three-Phase  Circuits,  Power  of 59 

Transformers. 

Auto,   for  Lamps      .........        8 

Constant  Current 36,    38 

Instrument         ..........      47 

Trimming  Arc  Lamps 13 

Troubles,   Arc  Lamp. 

Burned    Out   Coils 20 

Burned    Out   Economizer          .         .         .         .         .         .          .31 

Dirty   Carbons 13,    19 

Flaming     .         .         .         .         .         .         .         .         .          ...       19 

Globe    Blackening '.15 

Graphitization   of   Carbons       .         .         .         .         .         .         .18 

Jumping 19 

On    Arc    Lamp    Circuits          .         .         .         .          .         .         .43 

Operating  .         .         .         .         .         .         .          .         .         .21 

Poor    Light 17 

Reversed  Polarity 15,    30 

Short    Life 16 

Slipping  20,    32 

Twin  Carbon  Lamps 7 

Two-Phase  Circuits,   Power  of 59 

V 

Voltmeters,    Care    of 46 

Volumes   of  Geometrical   Figures 70 

w 

Water,  Weight  of 64 

Wattmeters,    Care  of 46 

Weights  of 

Building   Material 66 

Metals 65 

Water 64 

Wheatstone   Bridge,    Use   in   Locating  Faults        .         .  44 

Wire. 

Calculations    of    Size 52 

Carrying  Capacity  of  Copper — Table 55 

Properties    of    Copper — Table 56 

Wiring. 

Calculations    of    Size    of   Wire 52 

Constant  Current  Apparatus 37,  39 

Inside        ...........  48 

Switchboard,    Series   Arc    Lamp      ......  40 

Work,    Power   and    Force 58 

75 


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I 


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